12th Atmospheric Limb Workshop

22 May 2023, 09:00 → 26 May 2023, 12:10 Europe/Brussels

Palace of the Academies

It is with great pleasure that the ALTIUS team of BIRA-IASB invites you to the 12th Atmospheric Limb Workshop.

Dates: 22-26 May 2023

This event is generously sponsored by the Belgian Federal Science Policy Office (BELSPO), with additional sponsorship support from the European Space Agency (ESA) and Spacebel, and gourmet support from Rosalie's Chocolates.

The workshop will take place at the Palace of the Academies, located in the heart of Brussels, Belgium.

This is a scientific conference gathering research teams involved in the development and data processing of atmospheric limb missions. Past (e.g. SAGE-II, SCIAMACHY, GOMOS, MIPAS), current (e.g. SAGE-III/ISS, OSIRIS, OMPS-LP, ACE-FTS, MLS), and future (e.g. ALTIUS, MATS, CAIRT, CubeMap, SAGE-IV, ARGOS, ALI, SMR) Earth observation missions will be addressed at this workshop.

This 12th iteration of the workshop will have a new feature: we are offering to open the workshop to planetary limb missions (e.g. SOIR/VEx, NOMAD/TGO, OMEGA/MEx), so that scientists facing similar challenges on different planets can exchange ideas and techniques.

We look forward to seeing you in Brussels!

Monday, 22 May

14:00 → 16:00 Occultation: techniques, algorithms, products

14:40 Multi-wavelength dataset of aerosol extinction profiles retrieved from GOMOS stellar occultation measurements

In this work, we present the new multi-wavelength dataset of aerosol profiles, which are retrieved from the averaged transmittance spectra by the Global Ozone Monitoring by Occultation of Stars instruments on board the Envisat satellite.
Using monthly and zonally averaged transmittances as a starting point for the retrievals allows an improved signal-to-noise ratio of elimination of possible modulation of transmittance spectra by the incorrected scintillations. The two-step retrieval method is used: the spectral inversion is followed by the vertical inversion. The spectral inversion relies on removal on contribution from ozone, NO2, NO3 and Raileigh scattering from the optical depth spectra, for each ray perigee altitude. In the vertical inversion, the profiles of aerosol extinction coefficients at several wavelengths are retrieved from the collection of horizontally integrated aerosol extinction profiles.
The new aerosols extinction profiles (FMI-GOMOSaero dataset v.1) are provided in the altitude range 10-40 km at wavelengths 400, 440, 452, 470, 500, 525, 550, 672 and 750 nm, for the whole GOMOS operating period from August 2002 to March 2012.
The retrieved aerosol extinction profiles show realistic wavelength dependence. Validation has shown that FMI-GOMOSaero aerosol profiles are in good agreement with other datasets, and it has a better quality (i.e., wavelength-dependence, agreement with other datasets, enhancements during volcanic eruptions) compared to the previous GOMOS aerosol data.

Speaker: Viktoria Sofieva (Finnish Meteorological Institute)

15:00 Ozone in the Martian atmosphere observed by TGO/NOMAD-UVIS solar occultations.

Introduction: The NOMAD-UVIS instrument on board the ExoMars Trace Gas Orbiter has been investigating the Martian atmosphere with the occultation technique since April 2018 [1]. In the solar occultation mode, it is mainly devoted to study the climatology of ozone and aerosol content [2,3,4].
We analyzed almost two Mars Years of ozone vertical distributions acquired at the day-night terminator, corresponding to more than 8300 solar occultations, acquired between April 2018 (MY 34, LS=163°) and November 2021 (MY 36, LS=132°) [5].

Retrieval method(s): As in the work of [6], the NOMAD-UVIS ozone retrievals proved more difficult than expected due to the presence of spurious detection of ozone caused by instrumental effects, high dust content, and very low values of ozone. This leads us to compare the results from three different retrieval approaches:

1. an onion peeling method (OP);
2. a full occultation Optimal Estimation Method (FOEM), and
3. a direct onion peeling method (DOP).

The OP method is similar to that used for Mars and Venus stellar occultations [7,8]. The FOEM and DOP approaches are based on ASIMUT-ALVL, the BIRA-IASB radiative code [9,10].
The main challenge was to find reliable criteria to exclude spurious detection of O$_3$, and we finally adopted two criteria for filtering: i) a detection limit, and ii) the Δχ2 criterion. Both criteria exclude spurious O$_3$ values, especially near the perihelion, where based on the simulations from a general circulation model, we do expect very low values of ozone.

Comparison of filtering methods between UVIS and SPICAM:
We compared the results of filtering with SPICAM-UV observations. SPICAM is a UV spectrometer that has been observing the Martian atmosphere since 2004 on the Mars Express satellite. The SPICAM team applied very similar criteria for filtering their data to the ones implemented here [6]. Even if the two instruments observed the atmosphere during different Martian Years, the agreement on the filtered O$_3$ retrievals is very good, and both filtering approaches lead to very similar results.

The O$_3$-H$_2$O relationship: Water vapor was observed by the infrared channel of the NOMAD SO. The results from a first analysis can be found in [10], while an extended dataset is presented in [12]. Water vapor and ozone are measured simultaneously, which allows us to investigate the water-ozone correlation, the key to address the atmospheric chemistry on Mars.
We present correlation plots of O$_3$ vs. H$_2$O at high latitudes (60°-90°, both hemispheres), and the equator (30°S-30°N). It is important to notice that during a solar occultation experiment at the terminator, ozone may exhibit rapid changes due to photolysis that are uncorrelated to water vapor.

Impact of gradients at the Martian terminator: Rapid variations in species concentration at the terminator have the potential to cause asymmetries in the species distributions along the line of sight (LOS) of a solar occultation experiment. Ozone, in particular, displays steep gradients across the terminator of Mars due to photolysis [13]. Nowadays, most of the retrieval algorithms for solar and stellar occultations rely on the assumption of a spherically symmetrical atmosphere. However, photochemically induced variations near sunrise/sunset conditions need to be taken into account in the retrieval process in order to prevent inaccuracies.
We investigated the impact of gradients along the LOS for the retrieval of ozone under sunrise/sunset conditions. We used the diurnal variations in the ozone concentration obtained from photochemical model calculations together with an adapted radiative transfer code.

References: [1] Vandaele et al. (2015), PSS. [2] Patel et al. (2021), JGR (Planets). [3] Khayat et al. (2021), JGR (Planets). [4] Neefs, E., et al. (2015) Applied Optics. [5] Piccialli et al., ESS, accepted. [6] Määttänen et al. Icarus, Vol. 387, (2022), 115162. [7] Quémerais et al. (2006), JGR (Planets). [8] Piccialli et al. (2015), PSS. [9] Vandaele et al., (2008), JGR (Planets). [10] Piccialli et al. (2021), Icarus. [11] Aoki et al. (2019), JGR (Planets). [12] Aoki et al., (2022), JGR (Planets). [13] Lefèvre, et al. (2008), Nature.

Speaker: Dr Arianna Piccialli (BIRA-IASB)

15:20 Retrieval Methods and Measurements of Thermospheric Density and Temperature using SUVI Solar Occultations

Direct observations of the thermospheric state can provide direct indicators of space weather activity for constraining models of the thermosphere-ionosphere system. However, no such measurements are currently made in real-time for use in space weather operations, and few have been historically collected for research purposes.

Discussed are results from a NASA Operations to Research project to develop unprecedented operational measurements of the thermospheric state using the Solar UltraViolet Imager (SUVI) onboard the Geostationary Operational Environmental Satellite – R Series (GOES-R) constellation. SUVI images the Sun at extreme ultraviolet (EUV) wavelengths, with a primary objective to characterize and track the Sun’s morphology as it relates to the source of geoeffective space weather. Furthermore, since EUV radiation is strongly absorbed in the thermosphere, these measurements can also be used to probe the thermosphere during solar occultations. The wavelengths measured by SUVI provide sufficient constraints to distinguish the two major species of the middle and upper thermosphere: N2 and O. SUVI occulations cover all global latitudes over the course of a given occultation season, with occultation seasons occurring around the fall and spring equinoxes.

Presented here are methods illustrating how SUVI EUV images are converted to solar occultation light curves, and how density and temperature are derived from these light curves. In addition, example measurements made using these methods of thermospheric density, temperature, and composition from approximately 180 to 300 km are presented. Data from these measurements will be integrated into the GOES processing pipeline and publicly available on the NOAA National Centers for Environmental Information (NCEI) website, for occultations throughout SUVI’s expected operations from 2017 into the mid-2030s.

Speaker: Robert Sewell (CU Boulder/LASP)

15:40 SAGE III/ISS v5.3 Level 2 Data Product Changes and Improvements

The Stratospheric Aerosol and Gas Experiment on the International Space Station (SAGE III/ISS) is an occultation instrument that acquires measurements of aerosols and gases within the Earth’s stratosphere and upper troposphere. SAGE III/ISS provides level 2 solar species products for aerosol extinction (9 channels), nitrogen dioxide (NO2), ozone (O3), and water vapor (H2O). The level 2 products currently provide three O3 profiles based on differing retrievals. The first O3 profile is based on measurements at short wavelengths within the Hartley-Huggins band (MesO3), the second O3 profile is based on measurements made at visible wavelengths within the Chappius band (MLR O3), and the final profile is found using a more SAGE II like approach (AO3). The SAGE III/ISS also provides level 2 lunar species products for ozone (O3), nitrogen dioxide (NO2), and nitrogen trioxide (NO3).

Version 5.3 of the SAGE III/ISS retrieval algorithm introduces improvements that affect the level 2 data products. The largest change to the solar algorithm is the implementation of disturbance monitoring package (DMP) corrections to improve pointing accuracy. The DMP is comprised of a miniature inertial measurement unit that measures rotation in inertial space using ring laser gyroscopes oriented about three orthogonal axes which can be used to correct pointing errors caused by mechanical disturbances. A major change common to solar and lunar algorithms is meteorological input from the coarser 42 level Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) model data to the 72 level MERRA-2 model data. The final major change involves improving the automated quality assurance (QA) algorithm to recover events that were withheld from the public release because differences between the AO3 and MLR O3 for some events after the eruption of Tonga–Hunga Haʻapai. Other changes for v5.3 include minor bug fixes as well as restoration of some data quality flags that were removed in v5.21. This presentation presents the impacts of these changes as well as overall observations of interest from v5.3 level 2 data products.

Speaker: Carter Hulsey (SSAI)

14:00 → 14:40 Welcome speech

Speaker: Emmanuel Dekemper (BIRA-IASB)

16:00 → 16:30 Coffee break

16:30 → 17:10 Keynote talk: Occultation: techniques, algorithms, products

16:30 Mission Overview and Recent Results for the Atmospheric Chemistry Experiment (ACE)

The Atmospheric Chemistry Experiment (ACE) is comprised of a Fourier transform spectrometer (ACE-FTS) operating in the infrared with broad spectral coverage (750 – 4400 cm-1) and high resolution (0.02 cm-1), a UV-Visible-NIR spectrophotometer (ACE-MAESTRO, Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation) with wavelength coverage 280 – 1030 nm and resolution 1 – 2 nm, and a pair of imagers measuring at 525 and 1020 nm, respectively. Collecting solar occultation measurements since February 2004, ACE provides over 19 years’ worth of atmospheric profiles for pressure, temperature, and the volume mixing ratios of more than 30 molecules, as well as volume mixing ratio profiles for more than 20 subsidiary isotopologues. A mission overview will be provided, along with a description of the latest ACE-FTS processing version (version 5.0) and details of recent aerosol studies using ACE-FTS measurements.

Speaker: Chris Boone (University of Waterloo)

17:10 → 18:00 Occultation: techniques, algorithms, products

17:10 Mars atmosphere vertical profiles of carbon dioxide density and temperature from solar occultations recorded by the NOMAD instrument onboard ESA’s Trace Gas Orbiter

Although a drastic increase in missions to Mars, many atmospheric processes are still not fully understood such as gravity waves, thermal tides, and CO$_2$ ice clouds. Those processes can be monitored by the NOMAD instrument which regularly scans the atmosphere of Mars since April 21, 2018. The main purpose of NOMAD is the detection and distribution of trace gas but also to monitor the density and temperature of the Martian atmosphere [1].
The SO channel of the NOMAD instrument is dedicated to solar occultation measurements and thus probes the Martian terminator. It is an infrared spectrometer (2.3-4.3 µm) composed of an echelle grating coupled with an acousto-optic tunable filter (AOTF) for the selection of the diffraction orders.
Solar occultation measurement provides self-calibrated transmittance spectra [2]. The CO$_2$ density profiles are retrieved with the ASIMUT radiative transfer code and regularized with an iterated Tikhonov method [3]. The regularization is fine-tuned with the expected error estimation method [4]. By selecting the right diffraction orders, SO can monitor the CO$_2$ density from the troposphere to the upper thermosphere (0 to 200 km). Temperature can then be retrieved from the CO$_2$ density and the hydrostatic equilibrium equation, or the intensity of the CO$_2$ spectral signature.
Comparisons are ongoing with the GEM-Mars general circulation model [5, 6] and with datasets from other instruments such as MCS on Mars Reconnaissance Orbiter [7] and ACS also on Trace Gas Orbiter.
The latest results from those retrievals will be shown, such as CO$_2$ ice clouds which can be inferred in the mesosphere (50 to 100 km) from the temperature profiles when the values are lower than the limit for CO$_2$ condensation and the infrared signal decreases. Thermal tides are also constrained from profiles recorded in close ranges in solar longitude, local solar time, and latitude.

References : [1] Vandaele et al., (2015), PSS ; [2] Vandaele et al., (2008), JGR (Planets) ; [3] Quémerais et al., (2006), JGR (Planets) ; [4] Xu et al., (2016), JQSRT ; [5] Daerden et al. (2022), JGR (Planets) ; [6] Neary et al. (2020), GRL ; [7] Kleinböhl et al., (2009) , JGR (Planets); Alday et al. (2021a), Nature Astronomy.

Speaker: Loïc Trompet (BIRA-IASB)

18:00 → 20:00 Icebreaker

Tuesday, 23 May

09:00 → 09:10 Welcome and logistics

Speaker: Dr Noel Baker (BIRA-IASB)

09:10 → 10:30 Assimilation of limb products, and synergistic exploitation

09:10 GEOS Constituent Data Assimilation beyond Aura MLS: Assimilating NASA SAGE III/ISS profiles of stratospheric water vapor

Ozone and water vapor in the lower stratosphere are important trace gases for atmospheric chemistry and radiative budget. The Stratospheric Aerosol and Gas Experiment (SAGE) missions have been crucial in monitoring the stratospheric ozone loss and the subsequent recovery as well as the trends in water vapor linked to surface temperature trends. The SAGE III instrument aboard the International Space Station (ISS) continues the SAGE mission record, with high vertical resolution profiles of ozone and water vapor available since mid 2017. The NASA GEOS Earth system model has the new capability to assimilate multi-constituents from ground and space-based instruments using the GEOS Constituent Data Assimilation System (CoDAS). The recently released MERRA-2 Stratospheric Composition Reanalysis with Aura MLS (M2-SCREAM) assimilates version 4.2 MLS ozone, water vapor and other chemically-reactive species with the NASA GEOS model coupled to a stratospheric-only chemistry mechanism and transport constrained to the MERRA-2 reanalysis. While the number of solar occultation observations a day from SAGE III/ISS is about 1% of the total number of profiles observed globally by MLS, the chemical timescales of ozone and water vapor in the lower stratosphere are long enough that the SAGE III/ISS data may provide a useful constraint on the assimilated product. Using the same GEOS CoDAS configuration as M2-SCREAM, we will present a series of experiments to investigate if water vapor trends are consistent with the assimilation of SAGE observations with and without Aura retrievals, and to determine if the assimilation of SAGE observations produces a steady product for trend analysis, especially as the end of the Aura mission nears. In our experiments, assimilating only SAGE III/ISS water vapor profiles results in water vapor fields more consistent with experiments that assimilate MLS v5; however, in the polar regions SAGE III/ISS observations are not available and the modelled values are unconstrained. We are encouraged by the positive benefit assimilating the less frequent SAGE III/ISS observations has on stratospheric composition. Sensitivity experiments such as these will allow us to assess the added value of SAGE data for continued monitoring of the stratospheric composition for climate and ozone recovery assessments.

Speaker: Krzysztof Wargan (Global Modeling and Assimilation Office, NASA Goddard Space Flight Center)

09:30 Ozone CCI : recent science results and planned algorithm developments using limb/occultation data

ESA's Climate Change Initiative (CCI) programme was initiated around 2010 to address the difficulties in harmonising and merging climate data records (CDR) of Essential Climate Variables (ECV) and to provide climate modellers and researchers with stable long-term time series obtained by current and past European (and third-party) satellite missions. For over a decade now, the Ozone_cci team has been continuing the development of new/improved retrieval, harmonisation and merging algorithms for ozone measurements by limb- and nadir-viewing satellite sensors. Our climate data record portfolio (https://climate.esa.int/en/projects/ozone/data) consists of vertical ozone profile products and ozone column (total, troposphere) products, each of which was characterised through ground-based validation and several of which were assessed by climate researchers. Many of the products developed and matured within CCI have been transferred to the Copernicus Climate Change Service (C3S, https://cds.climate.copernicus.eu/cdsapp#!/dataset/satellite-ozone-v1) for operational processing, ensuring up-to-date ozone CDRs for the climate monitoring and climate research communities.

In this presentation, we highlight the importance of limb and occultation observations for existing and planned CCI ozone data products. We summarise recent science results inferred from the merged zonal mean (SAGE-CCI-OMPS+) and the merged 3D-resolved (MEGRIDOP) vertical ozone profile CDRs. This is followed by an overview of CCI algorithm development and validation analyses planned until mid-2024. A homogenisation scheme will be applied to Level-2 profiles from seven limb/occultations sensors to remove biases and to estimate random uncertainty a-posteriori. These homogenised profile data sets pave the way for two new gridded ozone CDRs (vertical profile, tropospheric column), covering two decades at high resolution (daily x 1° x 1°). The IUP-UB profile retrieval scheme will be applied to measurements by the recently launched OMPS-LP sensor onboard JPSS-2. We will prototype a scheme to combine these data with those from the OMPS instrument onboard SNPP. We conclude with a brief discussion of how the validation plan will be adapted to characterize these new CCI products using ground-based reference data and to verify their compliance with user requirements.

Speaker: Daan Hubert (Royal Belgian Institute for Space Aeronomy (BIRA-IASB))

09:50 The SWOOSH version 3.0 data set: Updates, their implications for variability and trends, and preparing for the loss of the Aura Microwave Limb Sounder

The Stratospheric Water and Ozone Satellite Homogenized (SWOOSH) database is a monthly mean merged data set of vertically resolved ozone and water vapor data from a subset of limb profiling instruments operating since the 1980s. In this presentation, we summarize recent updates and improvements to SWOOSH that were made as part of the forthcoming version 3.0 release. Changes in version 3.0 include updated versions of existing data sets, new sources of data, and additional ancillary information for quantifying uncertainties. We also assess the impact on variability and trends due to the source data updates (e.g., Aura MLS v5.0) and inclusion of new satellite records to SWOOSH from ACE-FTS, SAGE III/ISS, and OMPS-Limb Profiler. We also discuss plans to continue the SWOOSH record following the expected loss of the Aura MLS instrument in coming years, and the potential impacts of this loss on the uncertainty of the SWOOSH merged water vapor and ozone record.

Speaker: Sean Davis (NOAA Earth System Research Laboratory)

10:10 Studying transport and chemistry with the Stratospheric Composition Reanalysis of Aura Microwave Limb Sounder

NASA’s Global Modeling and Assimilation Office is producing a new reanalysis of stratospheric composition by assimilating water vapor, hydrogen chloride, nitric acid, nitrous oxide, and ozone profiles from Aura Microwave Limb Sounder (MLS). Named M2-SCREAM (MERRA-2 Stratospheric Composition Reanalysis of Aura MLS), this product covers the period between late 2004 and the present. Global three-dimensional fields of the assimilated species alongside winds, temperature, geopotential height and potential vorticity are provided at a three-hourly frequency and 50-km horizontal resolution. The vertical resolution in the stratosphere ranges between 1 and 2 km. The reanalysis output agrees well with independent data owing to the assimilation of high-quality vertically resolved MLS observations. The high frequency and resolution of the M2-SCREAM fields as well as the length of the record afford an opportunity to use the reanalysis in detailed studies of constituent transport and chemistry at a broad range of spatial and temporal scales. In this presentation we will briefly discuss preliminary analyses of several rare and extreme events observed in the stratosphere in recent years: water vapor plume from the eruption of Hunga Tonga – Hunga Ha’apai, chemical and dynamical perturbation of the Southern Hemisphere stratosphere from pyrocumulonimbus injections following Australian wildfires of 2019/2020, and tracer transport during the exceptional Arctic winter of 2019/2020. In all cases we will highlight the utility of the reanalysis for these studies and the importance of global limb data from MLS in providing rich spatiotemporal information in the reanalysis tracer fields. We will also discuss challenges that extreme events pose for data assimilation and for the use of limb observations in general.

Speaker: Krzysztof Wargan (Global Modeling and Assimilation Office, NASA Goddard Space Flight Center / SSAI)

10:30 → 11:00 Coffee break

11:00 → 11:40 Keynote talk: Upcoming limb instruments

11:00 The commissioning phase of the Swedish MATS satellite.

The MATS (Mesospheric Aerosol/Airglow Tomography and Spectroscopy) satellite was finally launched on 4 November 2022 aboard an Electron rocket from New Zealand. It entered a 585 km sun-synchronous orbit with an LTAN of 17:45. Already a few days after launch first light was seen by the instrument confirming its functionality and ability to collect the planned data.
MATS images the mesosphere region in two wavelength regions ; the UV at 270 and 304 nm and the IR in 4 channels around the 760 nm Oxygen A-band emission, The UV channels are used for studying small scale structures in Noctilucent clouds in the summer mesopause region using tomographic techniques while the IR channels provide global information on wave structures using the nightglow and dayglow emission from O$_2$(b).
We will present early data from the satellite commissioning programme illustrating the performance of the instrument and expected data products.

Speaker: Donal Murtagh (CHALMERS TEKNISKA HÖGSKOLA)

11:40 → 13:00 Upcoming limb instruments

11:40 The Stratospheric Aerosol and Gas Experiment (SAGE) IV

Atmospheric composition continues to be a key Earth science focus for international space agencies and research organizations. The target constituent varies depending upon the topic area of interest such as monitoring the ozone layer and the efficacy of the Montreal Protocol, assessing the influence of volcanic eruptions and large wildfires on the atmosphere, improving our knowledge of transport processes, or evaluating the impacts of greenhouse gases on climate. Additionally, there is a growing need for measurement continuity of many trace gases both from an inability to properly assess long-term trends without it as well as the reliance of reanalyses and chemistry climate models on observational input. To this end, proper continuity requires continuous and overlapping multi-instrument data records of which spaceborne measurements are a critical component. However, most current satellite systems are well beyond their expected lifetimes, and so we look toward the future to develop the Stratospheric Aerosol and Gas Experiment (SAGE) IV as a future mission concept. Enabled by the NASA Earth Science Technology Office’s (ESTO) Instrument Incubator Program, the SAGE IV Pathfinder project has developed and validated a prototype demonstration that paves the way for a future SAGE IV spaceflight mission. Utilizing solar occultation imaging, SAGE IV will be capable of measuring key species in the stratosphere and upper troposphere with the same quality as previous SAGE instruments but with greatly improved pointing knowledge and extensibility to new science targets. Furthermore, current technological advancements allow SAGE IV to fit within a CubeSat framework and make use of commercial hardware, significantly reducing the size and cost when compared with traditional missions and enabling sustainability of future measurements.

Speaker: Robert Damadeo (NASA Langley Research Center)

12:00 CubeMAP - Cubesats for Monitoring of Atmospheric Processes

The composition of the Upper Troposphere and Stratosphere (UTS) plays a significant role in controlling the Earth’s climate, but there are still poorly explored feedbacks within the Earth System. This region is coupled to the surface and the free troposphere both dynamically and radiatively. Its composition is strongly affected by anthropogenic emissions of greenhouse gases (GHG) and pollution precursors, and is subject to changes via radiative, dynamical, and chemical processes. As the Earth’s atmosphere is changing, so is the UTS. The rapid vertical and horizontal variations in the abundances of trace gases and aerosol around the tropopause, as well as strong and differing trends either side of the tropopause, have made trend detection challenging in this region with a knock-on effect on estimates of their climate impact.
The overall goal of CubeMAP (Cubesats for Monitoring of Atmospheric Processes) is to study, understand, and quantify processes in the UTS, study its variability, and contribute to analysis of trends in its composition and the resulting effects on climate and vice-versa. The mission focuses on tropical regions for at least two years, which are most critical for UTS processes, as the strong vertical transport in these latitudes means this is effectively the “gateway to the stratosphere”.
The space sector is also changing at a fast pace, which ought to benefit innovation for science missions, with faster, more agile development. CubeMAP embraces a high level of innovation to studies the UTS processes owing to a constellation-based sounding approach and miniaturized spectrometers that leverages small satellite benefits and obviate the limited coverage usually associated with solar occultation limb sounding.
An introduction to the mission and its status will be presented.

Speaker: Damien Weidmann (STFC Rutherford Appleton Laboratory (RAL Space))

12:20 Limb observations across scales: Examples of advances in airborne FTIR sounding and a glimpse of capabilities of proposed future space missions

Fourier-transform infrared (FTIR) sounding of the thermal emission of the Earth’s atmosphere is a versatile tool to address multiple scientific questions with one single instrument. Broad spectral coverage in combination with high spectral resolution provide information on a variety of trace gases, temperature and clouds. In the last decades, airborne FTIR sounders have been deployed for demonstration of technologies designated for space instruments, validation of implemented missions, and addressing distinct scientific questions. We present a brief selection of observations by the airborne limb sounder MIPAS-STR (Michelson Interferometer for Passive Atmospheric Sounding-STRatospheric aircraft), the airborne limb imager GLORIA (Gimballed Limb Observer for Radiance Imaging of the Atmosphere), the balloon-borne MIPAS-B instrument, and MIPAS onboard Envisat in the last decades together with further observations and model data. The presented results comprise observations of the Arctic polar vortex, populations of large nitric acid trihydrate particles in polar stratospheric clouds, the mesoscale fine structure of a tropopause fold, and gravity waves caused by merging jet streams. These studies illustrate how advances in airborne FTIR limb observations have enabled access to smaller scales and supported atmospheric research in a time, where important progress has also been made in chemistry transport modelling and weather forecasting. They furthermore provide a glimpse of what can be expected from proposed future space missions, such as the ESA Earth Explorer 11 candidate CAIRT (Changing-Atmosphere Infra-Red Tomography explorer).

Speaker: Wolfgang Woiwode (Karlsruhe Institute of Technology, Institute of Meteorology and Climate Research, Karlsruhe, Germany)

12:40 A nanosatellite instrument to measure temperature at the mesosphere and lower thermosphere boundary

A novel limb sounder for the measurement of temperature at the mesosphere and lower thermosphere boundary is presented. The instrument is designed to fly on Micro- and Nanosatellite platforms for the deployment in satellite constellations. The goal is to obtain a dense, 4-dimensional mesh of temperatures for resolving the small scale, time-varying waves that couple atmospheric regions.

The instrument’s core element is a spatial heterodyne interferometer, which is a monolithic Michelson-type interferometer, particularly suitable for harsh environments. The instrument successfully completed a student-led rocket mission and an in-orbit satellite technology demonstration. Upcoming deployments are within an international satellite program in research and education and an in-orbit demonstration and validation mission of the European Union. These missions will improve the maturity of the measurement concept based on extensive in-orbit characterizations.

Speaker: Martin Kaufmann (Reserach Centre Juelich)

13:00 → 14:00 Lunch

14:00 → 14:40 Keynote talk: Upcoming limb instruments

14:00 The Changing-Atmosphere Infra-Red Tomography Explorer CAIRT – a candidate for ESA’s Earth Explorer 11

The Changing-Atmosphere Infra-Red Tomography Explorer (CAIRT) is currently in Phase 0 as one of four candidates for ESA’s Earth Explorer 11. As a Fourier transform infrared limb imager, CAIRT will observe simultaneously from the middle troposphere to the lower thermosphere at high spectral resolution in 3D with unprecedented horizontal and vertical resolution. With this, CAIRT will provide critical information on the interaction of middle atmosphere circulation and composition, with a focus on (a) atmospheric gravity waves and mixing, (b) coupling with the upper atmosphere, solar variability and space weather and, (c) aerosols and pollutants in the upper troposphere and lower stratosphere. In this presentation we will give an overview of CAIRT’s science goals and the expected mission performance, based on latest results from Phase 0 studies.

Speaker: Björn-Martin Sinnhuber (Karlsruhe Institute of Technology)

14:40 → 16:00 Upcoming limb instruments

14:40 Observing System Simulation Experiment of the CAIRT ozone limb profiles focusing on stratosphere to troposphere exchange

The Changing-Atmosphere Infra-Red Tomography Explorer (CAIRT) is one of the four candidates for ESA’s Earth Explorer 11. This mission has been proposed in order to achieve a step change in our understanding of the coupling of atmospheric circulation, composition and regional climate. The CAIRT concept proposes to perform limb tomography of the atmosphere from the troposphere to the lower thermosphere (about 5 to 115 km altitude) with a swath between 300 and 500 km and having high spatial and spectral resolution to provide a three-dimensional picture of atmospheric structure at unprecedented scales.
This contribution will investigate the capability of CAIRT to analyse stratosphere to troposphere exchange using an Observing System Simulation Experiment (OSSE). In this effort, a reference atmosphere – the nature run in the OSSE terminology – is built based on the Copernicus Atmosphere Monitoring Services (CAMS) control run in 2021 (i.e. with a horizontal resolution ~40 km and a vertical resolution ~500 m in the tropopause region). The nature run is used to generate CAIRT ozone profiles, along with a CAIRT orbit simulator and a simulator to generate CAIRT ozone retrieval responses and error covariance matrix. Simulated CAIRT ozone profiles are then assimilated by the Belgian Assimilation System for Chemical ObsErvations (BASCOE) to provide ozone analyses – the assimilation run. In order to measure the added value of CAIRT data in the assimilation run, a BASCOE control run without CAIRT assimilation, is also done. Ozone fluxes across the tropopause are calculated from these three numerical experiments which will be discussed in this presentation.

Speaker: Quentin Errera (BIRA-IASB)

15:00 High-Altitude Water and Cloud satellite mission Part 1: Coincident limb observations of UTLS water vapour and aerosol combined with collocated nadir observations of cloud properties

The HAWC (High-altitude Aerosols, Water vapour and Clouds) mission is a highly synergistic observing system that showcases three Canadian instruments: the Aerosol Limb Imager, the Thin Ice Clouds in the Far InfraRed Emissions (TICFIRE) instrument, and the Spatial Heterodyne Observations of Water instrument. The mission was selected as the Canadian contribution to NASA’s Atmospheric Observing System; a satellite constellation proposed by NASA that includes multiple instruments to monitor aerosol, clouds, and precipitation as part of the Earth System Observatory (ESO). The HAWC instruments will work together to obtain limb measurements of aerosol and water vapour with nadir measurements of radiation, thin ice cloud content, and cloud microphysical properties. These coordinated measurements between the instruments will help build a more comprehensive picture of the high-altitude aerosol, cloud, and water vapour in the atmosphere. The first half of this talk will provide an overview of HAWC and the science objectives of the mission. The second half will focus on SHOW and the status of the instrument and algorithm development. A planned sub-orbital demonstration and validation flight on the NASA ER-2 for the fall of 2023 will also be discussed.

Speaker: Jeffery Langille

15:20 High-Altitude Water and Cloud satellite mission part 2: Instrument synergy and upcoming campaigns

HAWC (High-altitude Aerosols, Water vapour and Clouds) is a new Canadian mission with three instruments designed to measure aerosol, clouds, water vapour and radiation in the Upper Troposphere and Lower Stratosphere (UTLS). The Aerosol Limb Imager (ALI), focuses on aerosol and high clouds by taking two dimensional, multi-spectral images of Earth’s limb in the visible and near infrared to retrieve aerosol extinction profiles and particle size. With the ability to measure dual polarization states, ALI will also provide information on cloud top altitude and phase unprecedented from a limb viewing mission. The other limb viewing instrument on HAWC is the Spatial Heterodyne Observations of Water (SHOW), which will provide coincident, high resolution vertical profiles of water vapour. In the fall of 2023, ALI and SHOW will partake in an ER-2 aircraft campaign to test the instruments and retrieval algorithms. This work will present an overview of the ALI instrument and the science enabled through the coordinated retrievals with SHOW and the upcoming aircraft campaign.

Speaker: Landon Rieger

15:40 The Airborne Scanning Microwave Limb Sounder (A-SMLS)

The Airborne Scanning Microwave Limb Sounder (A-SMLS) is an instrument designed to fly onboard the NASA ER-2 aircraft, making wide-swath vertical profile observations of the composition of the upper troposphere and lower stratosphere (~10 – 20 km altitude) at 340 GHz. Observing a ~300km-wide swath ahead of the aircraft in a 2D raster scan (azimuth and elevation), A-SMLS is designed to measure water vapor, ozone, and carbon monoxide with a 10 x 10km horizontal resolution (across and along-track).

A-SMLS is well suited for deployment to study convective outflow, long-range pollution, and volcanic emission transport, as well as the exchange of air between the troposphere and stratosphere. As such, A-SMLS observations from the ER-2 will prove to be a valuable asset in future multi-instrumental field campaigns. For example, utilizing the wide swath to provide context for more detailed measurements by lower altitude aircraft.

A-SMLS was originally developed for the WB-57 and has now been adapted to fit the ER-2. Upgrades to the detector cooling system and adaptive mirror pointing control are in progress. The current expected performance of A-SMLS, as well as the latest development and upgrades to the instrument will be presented, in advance of planned flights later in 2023.

Speaker: Frank Winiberg (Jet Propulsion Laboratory, California Institute of Technology)

16:00 → 16:30 Coffee break

16:30 → 17:30 Upcoming limb instruments

16:30 Limb Scattering Measurements of Stratospheric Aerosols With ARGOS

Characterizing the distribution and evolution of aerosol particles in the stratosphere (10-40 km altitude) is important for understanding their potential contribution to long-term climate through heating. Significant heating effects are also observed due to impulsive events such as volcanic eruptions and smoke plumes from large wildfires, which can have considerable economic consequences. These aerosols are currently monitored using limb measurements from instruments such as SAGE III/ISS, OSIRIS, and OMPS LP. We have developed a compact instrument called Aerosol Radiometer for Global Observations of the Stratosphere (ARGOS) in order to improve the sensitivity and spatial coverage of these aerosol data. The instrument optical design has no moving parts to increase reliability, and uses a central prism to make limb viewing measurements of the atmosphere in eight directions simultaneously with a single detector. The combination of forward-viewing and backward-viewing measurements along the orbit track will provide good sensitivity at all latitudes, as well as near-simultaneous samples for specific locations at different scattering angles to help constrain the aerosol phase function. ARGOS uses two wavelengths in the near-IR spectral region (870 nm, 1550 nm) to extend altitude coverage and provide information on the particle size distribution. ARGOS is scheduled for space flight demonstration in Spring 2024 as a hosted payload supported by Loft Orbital. This approach offers significant advantages for small instruments in terms of available size, mass, power, communications, mission operations, and flight opportunities. We will discuss the current status of ARGOS development.

Speaker: Mr Matthew DeLand (Science Systems and Applications, Inc.)

16:50 Initial performance results of the NOAA-21 OMPS Limb Profiler instrument

The Ozone Mapping and Profiler Suite (OMPS) that launched in November 2022 on the NOAA-21 satellite contains the second in a series of NASA Limb Profiler (LP) instruments to be launched through 2034. The NOAA-21 LP has the same basic design as the SNPP LP operating since 2012 but includes several enhancements to improve stray light performance, reduce noise, and remedy some troubling thermal sensitivities of the earlier build. Stray light improvements at NIR wavelengths were emphasized because of their importance for aerosol extinction retrievals. Steeper atmospheric vertical signal gradients at long wavelengths result in enhanced contamination from internally-scattered photons, which is especially problematic at altitudes used by the retrievals for radiance normalization.

In this presentation we will describe the instrument changes and present initial performance results from the NOAA-21 instrument including, but not limited to, vertical coverage, pointing accuracy, out-of-field and out-of-band stray light, and the effects of vertical aliasing due to spacecraft motion. Where possible we compare the NOAA-21 instrument performance to that of the SNPP instrument. Such comparisons are helpful for discriminating between instrumental and geophysical phenomena observed in the data product.

Speaker: Glen Jaross (NASA/GSFC)

17:10 The Continuity Microwave Limb Sounder (C-MLS) – Capitalizing on New Technology to Continue the MLS Record of Daily Global Middle Atmosphere Composition Observations.

Spaceborne observations have enabled critical insights into the behavior of Earth's atmosphere. Atmospheric limb sounding (viewing the atmosphere edge-on) offers good vertical resolution, and the long atmospheric path viewed provides a strong signal to noise for measurements of tenuous trace gases. We present an overview of the “Microwave Limb Sounder” (MLS) series of instruments, whose measurements have been used in studies of issues related to stratospheric ozone layer stability, climate variability and change, and the impact of stratospheric ozone on air quality. To date, more than 1700 peer-reviewed publications have used data from the MLS instruments on NASA’s Upper Atmosphere Research Satellite (UARS, 1991–2000) and Aura (2004–) missions.

We briefly review the MLS technique and the MLS instrument on Aura, then describe a new “Continuity-MLS” instrument under development. Continuity MLS obtains nearly all of the measurements made by Aura MLS, but in a far more compact form factor (60kg, 80W vs. 500kg, 500W). Continuity-MLS takes advantage of new advances in microwave technology, including singlechip digital spectrometers and compact ~100 GHz oscillators. The C-MLS instrument is a strong candidate for the “Ozone and Trace Gas” opportunity that is part of NASA’s new “Earth Explorer” program. It would also ideally suited to NASA’s new “Earth Venture-Continuity” opportunity.

Speaker: Frank Winiberg (NASA Jet Propulsion Laboratory, California Institute of Technology)

17:30 → 19:30 Poster session #1

17:30 An assessment of the SAGE III/ISS temperature and pressure research products

The Stratospheric Aerosol and Gas Experiment (SAGE) III instrument was deployed on the International Space Station (ISS) in early March 2017 and began routine measurements in June 2017. SAGE III retrieves profiles of temperature and pressure from multi-spectral measurements of the oxygen A-band absorption feature centered near 762 nm. The A-band is located in a favorable spectral region where molecular oxygen is the dominant absorber with only minor contributions from ozone absorption, Rayleigh scattering, and aerosol extinction. Since the vertical distribution of molecular oxygen is well known, variations in the measured A-band spectra reveal information about the temperature and pressure structure of the atmosphere. Temperature/pressure products from the predecessor SAGE III METEOR/3M mission were of limited science value due to instrument issues. The SAGE III/ISS oxygen A-band spectra are of higher fidelity than those from the METEOR/3M instrument and the initial temperature/pressure products are in reasonable agreement with MERRA-2 (Modern-Era Retrospective analyses for Research and Applications, Version 2) data. Additional refinements to wavelength registration and forward model parameters have improved the overall quality of the products. In this paper, we will present an overview of the temperature/pressure retrieval approach, results of the forward model studies, and an assessment of the quality of the temperature and pressure research products through comparisons with correlative measurements.

Speaker: Michael Pitts (NASA Langley Research Center)

17:30 Are trends in total ozone consistent with stratospheric ozone trends from satellite observations?

Total ozone is a measure of the protection of the biosphere from UV radiation. Extratropical total ozone recovery trends of about +0.5%/decade are consistent with the continuous decline in stratospheric halogen loading since the middle 1990s as a consequence of the Montreal Protocol and its Amendments on phasing out ODS. Nevertheless, the recovery (or chemistry-related) trends in the northern hemisphere (NH) are compensated by changes in atmospheric dynamics leading to stable ozone levels since about 2000 (apart from year-to-year variability). The near-global (60°S-60°N) average total ozone level is currently about 2-3% below the 1964-1980 mean.

Lower stratospheric ozone, the dominating contributor to the total ozone column and derived from limb satellite observations, shows globally (below 60° latitude) a slightly negative (but mostly statistically insignificant) trend of about -1.5%/decade since 2000, which is not consistent with the stable total ozone levels in the NH. Some studies suggested that increases in tropospheric ozone compensate for negative lower stratospheric trends leading to stable column levels. The trend regression models applied to ozone profiles and total ozone also differ. For instance, proxies representing changes in atmospheric dynamics and transport have been included for total ozone, but not for ozone profiles, which may also lead to inconsistencies between total and stratospheric column trends.

This presentation will report updated total ozone trends from five merged total ozone datasets up to 2022. The same regression model, including proxies representing atmospheric dynamics and transport, will be then applied to ozone profiles from the merged limb dataset (SAGE II-SCIAMACHY-OMPS) to evaluate the consistency between column and profile trends.

Speaker: Mark Weber (University of Bremen)

17:30 Comparison of merged ozone profile datasets and resulting ozone trends

Stratospheric ozone absorbs ultraviolet radiation that is harmful to life on earth. Ozone is a major driving force of atmospheric dynamic processes and is responsible for the radiative heating of the stratosphere. Due to anthropogenic emissions of ozone-depleting substances (ODS) the amount of
stratospheric ozone decreased substantially through the latter part of the 20th century and the so-called ozone holes were observed. The Montreal Protocol in 1987 and later Amendments banned ozone-depleting substances (ODS) in order to stop the ozone decline and facilitate its recovery. The
speed and occurrence (location) of ozone recovery depends not only on the declining amount of ODS but also on atmospheric dynamics and radiative budget and thus is related to the variations in greenhouse gases.

To assess changes in global ozone and attribute processes responsible for these changes, long-term observational time series of ozone are needed. Currently, several merged datasets are available, e.g. GOZCARDS, SWOOSH, SAGE-CCI-OMPS and SAGE-SCIA-OMPS. These datasets comprise measurements from various space-borne instruments over many years (here more than 30 years).

Differences in ozone units and vertical grids are an issue when comparing different datasets. In this work, the ozone data sets are homogenized by converting them to the same units and vertical grids. The uncertainty associated with these conversions is assessed. Using the homogenized merged datasets, we compare the ozone time series and trends in stratospheric columns and vertical profiles of ozone. Long-term trends are estimated using different statistical techniques such as multiple linear regression (MLR), dynamical linear (DLM) regression models. We also use Chemical Transport Model (CTM) simulations with different chemical and dynamical settings to gain better insight about the estimated ozone trends.

Speaker: Brian Auffarth (Universität Bremen)

17:30 Detection of transients in OMPS Limb Profiler earth view data

The detection of random transients, arising from high energy particle hits on CCD pixels, bears significance for the OMPS Limb Profiler (LP) sensor and other limb scatter sensors of similar design. This is because majority of the LP science data products are derived from altitude normalized radiances where even small transients at normalization altitude can be significant. Results from a transient detection algorithm employing principal component analysis (PCA) of LP earth view data are presented. The algorithm is shown to be reasonably successful in detection and flagging of significant transients which on a daily global map predominantly occur over South Atlantic Anomaly (SAA) region, and with few detections happening outside the SAA region. The detections outside SAA region are linked to unique geophysical phenomena characterized by vertical-temporal correlations and are considered as false positives from a transient detection perspective except for rare occurrences of transient hits from geomagnetic activities mostly confined to polar regions. An additional feature of the algorithm is the ability to offer predicted radiance as an option to the user to replace values adversely affected by transients. The details of the algorithm, methodology of analysis and results are presented.

Speaker: Rama Varma Raja M. K. (Science Systems and Applications,Inc.)

17:30 ENSO and IOD signatures in the tropical Upper Troposphere Lower Stratosphere Ozone

The combined effect of El Niño-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD)on the tropical Upper Troposphere Lower Stratosphere (UTLS) ozone is examined using the data from Microwave Limb Sounder (MLS) onboard Aura Satellite and ECMWF (European Centre for Medium-Range Weather Forecasts) ERA5 reanalysis. During the years of positive (negative) ENSO and IOD events, UTLS ozone mixing ratio shows a decrease (increase) in the absolute values. We also analyse the Quasi-Biennial Oscillation (QBO) which shows an in-phase variation with the ozone anomaly. The calculated eddy heat flux (used as a proxy for Brewer-Dobson Circulation, also known as BDC) corroborates the positive (negative) ozone anomaly by the high tropical downwelling (upwelling). To quantify the contributions of ENSO,IOD, and QBO –in the observed ozone anomaly, multivariate linear regression (MLR) analysis is performed using the least square method. It shows that one fourth of the observed ozone variation during the period of study (2005-2020) can be attributed to ENSO, IOD, and QBO altogether. This preliminary study suggests that large scale climate drivers from the Pacific and the Indian ocean should be considered while examining the UTLS ozone distribution.

Speaker: Dr OINDRILA NATH (BIRA-IASB)

17:30 Grist in the sausage: how OMPS Limb PSFs are characterized to make palatable data products

The Ozone Mapping and Profiler Suite’s Limb Profiler (OMPS-LP), built by Ball Aerospace, is a dedicated imaging spectrograph for measuring vertical ozone profiles. Two Limb Sensors are currently in orbit aboard the Suomi NPP and JPSS-2 (now NOAA-21) spacecraft with two more units slated to fly aboard JPSS-3 and JPSS-4. The Limb sensor measures the vertical distribution of ozone in the atmosphere by measuring the spectral radiance of Earth’s limb from the horizon to ~120 km over the 290nm to 1000nm spectral range. The largest uncertainty in Limb-generated science is caused by stray light contamination. This presentation will detail the testing, modelling, and analysis required to characterize stray light performance, focusing on the sensor’s Point Spread Function (PSF). This characterization is critical for generating quality stray light corrections to on-orbit data. We will also compare the stray light performance of the different Limb Sensor builds (NPP thru J4) as well as the sensor design changes which have contributed to the steadily improving performance.

Speaker: Dr Thomas Rogers (Ball Aerospace)

17:30 GSLS radiative transfer model updates and preliminary assessment of their effect on the OMPS LP aerosol retrieval

This presentation describes recent updates to the Gauss Seidel Limb Scattering (GSLS) radiative transfer model, and provides a preliminary assessment of the impact of those updates on the NASA OMPS LP aerosol extinction coefficient retrieval algorithm. This work builds upon the most recently-released aerosol extinction data product (Version 2.1), which provides retrievals at several wavelengths from 500 – 1000 nm.

Speaker: Ghassan Taha (MSU/NASA GSFC)

17:30 Implementation of sulfur hexafluoride (SF$_6$) in the Belgian Assimilation System for Chemical ObsErvations

Sulfur hexafluoride (SF$_6$) is a greenhouse gas that is emitted at the surface because of its use as an insulator in electrical transmission equipment and electronic devices. Since its quasi-linear emission growth and its very long lifetime, SF$_6$ can be used as a tracer for the Age of Air (AoA) to diagnose changes in the Brewer Dobson Circulation (BDC). The chemistry of SF$_6$ has been implemented in the Chemistry Transport Model (CTM) of the Belgian Assimilation System for Chemical ObsErvations (BASCOE). Reaction rates were taken from previous studies while an electron density has been taken from WACCM-X-SD simulations.
In this contribution, BASCOE-CTM simulations driven by ERA5 and MERRA2 will be discussed considering SF$_6$ with and without mesospheric sinks (i.e. passive SF$_6$ in the latter case). During the course of the simulations, the computed mixing ratios have also been saved in the space of MIPAS observations to analyse the impact of the MIPAS sampling in its AoA derivation.

Speaker: Sarah Vervalcke (BIRA-IASB)

17:30 LOTUS Highlights on Ozone Trend Analyses and Future Direction

LOTUS (Long-term Ozone Trends and Uncertainties in the Stratosphere) is a SPARC (Stratosphere-troposphere Processes And their Role in Climate)-sponsored effort to foster collaboration between established and early career scientists around the world, with expertise in ozone observations, modeling, and trend tools, with an aim toward innovating new climate research that meets the needs of the ozone trends community and provides vital contributions to the WMO Assessment in an organized and cohesive way. Here we will summarize recent studies associated with the LOTUS effort that perform trend analyses on both total column and vertical profiles of ozone. The main findings of the derived trends from both observations and chemistry climate models have important implications for the status of the ozone layer as they pertain to the efficacy of the Montreal Protocol. These results also present new questions and knowledge gaps that will be outlined as areas of future study in Phase 3 of the LOTUS effort over the next few years to inform the next Assessment.

Speaker: Robert Damadeo (NASA Langley Research Center)

17:30 OMPS Limb Profiler Stray Light Updates on SNPP and NOAA-21

The Limb Profiler (LP) instrument, part of the Ozone Mapper and Profiler (OMPS) Suite, is designed to measure ozone and aerosol vertical profiles in the stratosphere and to continue long-term ozone data records. The first OMPS LP instrument has been operating on the Suomi National Polar-orbiting Partnership (SNPP) satellite since 2012 and the second LP instrument on the NOAA-21 satellite was launched in November 2022. Although the OMPS LP stray light error does not have a strong influence on the retrievals of stratospheric ozone, it is important for high altitude temperature, mesospheric ozone and stratospheric aerosol profiles. The in-flight stray light is calculated and removed before signals are converted to radiance (or irradiance) with a stray light source and target Jacobian matrix. The correction matrix is based on ground test Point Spread Functions (PSFs) but also been updated for the SNPP LP instrument using in-flight results. In this presentation we will show the stray light updates in SNPP LP product version v2.6 compared to the previous version.

Several design changes to improve stray light performance were made in the second LP instrument, including a modified detector coating and larger spectral/spatial separation of images at the focal plane. By comparing the stray light in UV, Visible and near-IR channels of NOAA-21 and SNPP, we will show the effectiveness of these design updates.

Speaker: Grace Chen (Science Systems and Applications, Inc, GSFC, NASA)

17:30 OSIRIS on Odin: Over Twenty Two Years of Measurements

The OSIRIS instrument has now operated for over 20 years beyond its original two year lifetime and there are no technical reasons why it will not continue to operate for at least the next few years. The Team associated with this Canadian built instrument was part of the initial consortium of scientists that pioneered the concept of these ongoing Limb Workshops. This presentation will summarize the history of OSIRIS and outline some of the many scientific accomplishments made possible with OSIRIS data. It will also give an update on the current status of OSIRIS and introduce the community to some of the new OSIRIS Team.

Speaker: Mr Taran Warnock (University of Saskatchewan)

17:30 Particle size distribution from SCIAMACHY limb observations: 2-parameter vs. 3-parameter retrieval

Stratospheric aerosols play a key role in atmospheric chemistry and climate. They are considered a catalyst for ozone depletion, serve as condensation nuclei for polar stratospheric cloud formation, and, in large quantities, have a short-term impact on the Earth's radiative budget. The aerosol effects depend strongly on the aerosol particle size distribution (PSD). Despite its importance, available observations on aerosol particle size are rather limited, restricting the knowledge of chemical and climate aerosol feedback mechanisms. An extension of the PSD data set is therefore desirable.

We retrieve the PSD from SCIAMACHY (Scanning Imaging Absorption Spectrometer for Atmospheric Cartography) limb observations. The retrieved PSD profiles are compared with in-situ balloon-borne measurements from Laramie, Wyoming, and SAGE III-M3M (Stratospheric Aerosol and Gas Experiment III onboard the Russian Meteor-3M) retrievals over the northern hemisphere. Assuming a fixed number density profile, the median radius and geometric standard deviation from SCIAMACHY, balloon-borne measurements, and SAGE III agree within about 27 % and 10 %, respectively. A more accurate a priori number density profile can usually reduce the differences by more than a factor of two.

The simultaneous retrieval of three PSD parameters, i.e., median radius, geometric standard deviation, and number density, from SCIAMACHY limb observations can potentially reduce retrieval errors. The median radius, geometric standard deviation, and the number density deviate by less than 15 %, 6 %, and 40 % from the balloon-borne measurements. Actual comparisons to PSD retrievals from SAGE III-M3M will be presented.

Speaker: Christine Pohl

17:30 Projecting the Lasting Fate of the Hunga Tonga-Hunga Ha’apai Eruption on the Stratosphere through Connecting Measurements to Models

On 15th Jan. 2022 the submarine volcano Hunga Tonga-Hunga Ha’apai (HTHH) injected approximately 0.5 Tg of sulfur dioxide into the stratosphere, but more significantly added 150-170 Tg of water vapor to the stratospheric background (over a 10% perturbation) in a matter of several hours. The sulfur dioxide rapidly converted to sulfate aerosol and along with water vapor, was transported around the Southern Hemisphere sub-tropics into midlatitudes with some transport into the Northern Hemisphere. With a much longer lifetime than sulfate aerosol, measurable water vapor anomalies are likely to persist for the remainder of the decade. Satellite measurements from limb and nadir viewing observing instruments provide the information needed to reasonably initialize the HTHH eruption in the Goddard Earth Observing System (GEOS) model using the “replay” framework coupled to the Global Modeling Initiative (GMI) stratosphere-troposphere chemical mechanism for the recent past and continue the simulations into the future with the free running chemistry climate model (CCM). Using a number of model ensemble members together with the satellite observations, we are beginning to quantify how the HTHH eruption is perturbing stratospheric composition and climate and projecting the influences to come as the enhanced water vapor continues to spread globally with only very slow removal mechanisms. We will also discuss some of the future measurement needs to understand how the atmosphere is responding to events like the HTHH eruption, large wildfires, and a changing climate.

Speaker: Dr Luke Oman (NASA/GSFC)

17:30 Temperature Profiles Derived from OMPS Limb Profiler

We have recently developed an algorithm to retrieve mid-stratospheric and lower mesospheric temperature profiles from the OMPS Limb Profiler (LP) sensor that has been flying on NOAA’s Suomi NPP Satellite since Oct 2012. The algorithm uses LP measured radiances at 11 wavelengths centered at 350 nm to retrieve atmospheric temperature profiles between 35-65 km at ~2 km vertical resolution with 1 km step. Comparison to other measurements indicates that the profiles have about +/- 2 K accuracy between 35 and 65 km with reduced accuracy above 65km. By vertically integrating the profiles using the hydrostatic equation starting with 35 km pressure from assimilated meteorological data we also obtain accurate pressure and density profiles up to 65 km. These profiles can be used to create a pressure reference for LP O3 measurements. They also remove the need for pairing short UV wavelengths with 350 nm to derive mesospheric ozone profiles from LP and can be used for improving altitude registration of LP. We will discuss these applications in our presentation.

Speaker: Zhong Chen (SSAI, USA)

17:30 The SASKTRAN Radiative Transfer Model

The SASKTRAN radiative transfer model has been used for over twenty years in the retrieval processes associated with the Canadian OSIRIS instrument in operation onboard the Swedish spacecraft Odin. It started as a single Rayleigh scatter model first developed in the mid-1990s and has evolved into something much more. This presentation will detail the latest SASKTRAN developments that make it useful for a wide variety of remote sensing applications that range from A-Band emissions measured with the Swedish instrument MATS, to nadir emission in the thermal infrared measured by a new Canadian concept, NH3Sat. SASKTRAN is fully documented and readily available for use by all scientists in the atmospheric remote sensing community.

Speaker: Doug Degenstein (University of Saskatchewa)

17:30 Upper tropospheric – lower stratospheric aerosol extinction retrieval from ground based twilight sky brightness measurements: the method and results.

During the twilight event the boundary between the illuminated and shadowed parts of the atmosphere shifts upward with the increasing solar zenith angle. This makes it possible to retrieve the vertical profile of aerosol extinction from the ground – based measurements of the twilight sky brightness as a function of the solar zenith angle, performed in a narrow field of view and a narrow spectral range.
The twilight sky brightness measurements were carried out in Georgia, South Caucasus and Belgium in the periods after the Pinatubo eruption in 1991 as well as Nabro, 2011 and Raikoke, 2019 eruptions. The extinction profiles retrieved from selected measurements illustrate the capability of the method. The Levenberg-Marquardt retrieval algorithm with the forward model based on the fully spherical Monte Carlo code Siro (developed in FMI) was used for the retrieval. Beside of the stratospheric aerosols, aerosol extinction enhancements in the troposphere were observed during a few saharan dust transport events.
Further development of the experimental equipment and the retrieval method will be discussed. Some advantages of observing twilight phenomena from satellites, especially for ALTIUS, will be considered.

Speaker: Nina Mateshvili (Royal Belgian Institute for Space Aeronomy)

17:30 Using Nonlinear Principal Component Analysis to Model the Quasi-Biennial Oscillation

The quasi-biennial oscillation (QBO) represents a significant component of atmospheric dynamic variability in the stratosphere. Disruptions in the regular, if complex, nature of the QBO observed beginning in 2015 have reduced the power of traditional modeling approaches using linear dimensionality reduction techniques, e.g. principal component analysis (PCA). While the use of additional principal components in trend analyses can increase efficacy, shortcomings may be present in the traditional approach given the unprecedented behavior observed in the last decade. A nonlinear PCA (NLPCA) approach is an option for representing multidimensional variance in nonlinear regimes while retaining the ability to extract linear and non-linear structures from data. NLPCA can potentially represent nonlinear perturbations present in the QBO and adequately account for resulting atmospheric impacts. The method presented implements an auto-associative neural network (AANN) which is a multi-layer feed-forward network. The AANN is trained by adjusting neuron weight (coefficient) values to minimize the loss between the original dataset and the reproduction using the limited number of neurons in a series representing encoding, compressive, and decoding layers. A python package has been created to implement NLPCA using an AANN with applicability geared toward atmospheric datasets and data structures. Assessments are performed using models of ozone concentrations, and comparisons between linear and nonlinear PCA coefficient QBO representations is performed using seasonal time series analysis and trending techniques.

Keywords: nonlinear principal component analysis, quasi-biennial oscillation, auto-associative neural network, ozone

Speaker: Mary Cate McKee (NASA/SSAI)

Wednesday, 24 May

09:00 → 09:10 Welcome and logistics

Speaker: Dr Noel Baker (BIRA-IASB)

09:10 → 10:30 Trace gases: profiles, trends

09:10 ACE-FTS water vapour trends in the stratosphere-mesosphere

The Atmospheric Chemistry Experiment`– Fourier Transform Spectrometer (ACE-FTS) is a high spectral resolution spectrometer on the SciSat satellite that has been taking solar occultation measurements of the Earth’s limb since February 2004. ACE-FTS measures vertical profiles of temperature/pressure and concentrations of over 60 trace gases, including ozone and water vapour, with a vertical resolution of ~2-6 km. From the beginning of the mission, ACE-FTS water vapour data exhibits a significant positive trend on the order of a few percent per decade throughout the stratosphere and mesosphere, in agreement with similar measurements from the Microwave Limb Sounder (MLS) and the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instruments. This study will investigate the link between ACE-FTS water vapour trends and decadal variations in other atmospheric parameters, including local and tropopause temperatures, ozone and methane concentrations, and solar flux, and will discuss how ACE-FTS measurements of HDO can be used to continue measuring background water vapour trends post-eruption of the Hunga Tonga-Hunga Ha’apai volcano, which injected ~160 Tg of water vapour (more than 10% of the stratospheric water vapour budget) into the stratosphere.

Speaker: Patrick Sheese (University of Toronto)

09:30 Lower stratospheric ozone trends from updated GOZCARDS data record and GMI model simulations

Both satellite observations and model simulations have shown ozone recovery since late 1990s. It is less certain for ozone in the mid-latitude lower stratosphere, where merged satellite observations suggest small decreases for 2000-2020, while Chemistry Climate Models (CCMs) suggest small increases (WMO, 2022). The differences could result from uncertainties in merged satellite data sets and/or deficiencies in CCMs. For example sampling biases in merged satellite data sets and how well CCMs simulate the impact of greenhouse gases (GHGs) and ozone-depleting substances (ODS) on Brewer-Dobson Circulation (BDC). We will update GOZCARDS ozone data record by including the latest SAGE III/ISS v5.30 and OMPS LP v2.6 data, and correcting sampling biases for sparsely sampled satellite measurements. This can provide more robust ozone trends with smaller uncertainties and extend GOZCARDS ozone data record when Aura mission is ended. Simulations from GMI (Global Modeling Initiative) CTM (Chemical Transport Model) and GEOS-5 general circulation model in replay mode will be used to further investigate the differences between observations and CCMs, and to attribute observed ozone trends in the mid-latitude lower stratosphere. Both the GMI CTM and GOES-5 in replay mode are driven by MERRA-2 meteorology, which can provide more realistic dynamics and inter-annual variability compared to CCMs.

Speaker: H.J. (Ray) Wang (Georgia Institute of Technology)

09:50 Variability and trends in three stratospheric water vapour profile data records

Uncertainties in observations often considerably limit our ability to assess long-term changes in the vertical distribution of water vapour. ESA's Climate Change Initiative (CCI) was set up to address the difficulties in harmonizing and merging climate data records (CDRs) of key climate variables and to provide climate modellers and researchers with high-quality, stable, long-term time series from current and past European (and third-party) satellite missions. As part of the CCI Water Vapour project, two vertically resolved water vapour data records have been developed (https://climate.esa.int/en/projects/water-vapour/data). The first product, CCI WV-strato, provides monthly zonal mean data in the stratosphere and lower mesosphere, combining observations from limb emission, scattering and occultation sensors. The second product, CCI WV-UTLS, is a three-dimensional monthly mean data record covering troposphere and UTLS, merging limb and nadir measurements.

In this contribution, we focus on the recently released CCI WV-strato (v3.3) and assess its potential for climate applications through a comparison to other recent CDRs, such as NOAA’s SWOOSH v2.7b and NASA’s GOZCARDS v1.10. We summarize the differences in input data, merging approach and general characteristics of these data records. All time series were analysed using regression techniques to infer multi-annual mean, seasonal cycle, quasi-biennial oscillation and long-term trends of water vapour across the stratosphere. For CCI WV-strato, the trend estimates are somewhat sensitive to the choice of quality flag applied for data screening. We present the coherence of the spatial structure of the parameters estimated from all three CDRs. We find that the magnitude and the spatial structure of the temporal (quasi)cycles are very similar. Residual long-term water vapour changes are modelled as a piecewise continuous linear function with two change points, in January 1998 and January 2004. The sign of the trend in the three periods generally agrees well between CDRs. However, trend values for the 1998-2003 and 2004-2019 periods differ significantly between CDRs in certain regions of the stratosphere. We relate these differences to, for example, differences in contributing sensors and data versions. In conclusion, ESA's vertical-resolution CCI data sets on water vapour provide valuable new independent sources of information for long-term global studies and climate applications.

Speaker: Daan Hubert (Royal Belgian Institute for Space Aeronomy (BIRA-IASB))

10:10 Creating long-term climate data records using transfer functions

We present the calculation of ozone trends from various versions of combined satellite records SAGE II, MIPAS and OMPS NASA, which spans the period from 1979 to 2022. The merging is performed using different transfer standards: satellite records of ACE-FTS and MLS, and model runs EMAC, CMAM and WACCM. The impact of transfer standard on corresponding trends is investigated.

Speaker: Alexandra Laeng (KIT, Germany)

10:30 → 11:00 Coffee break

11:00 → 13:00 Trace gases: profiles, trends

11:00 Stratospheric NO2 profile climatology for OMPS LP

Nitrogen dioxide (NO2) has absorption lines in UV and VIS spectral windows and can interfere with the ozone retrievals derived from Ozone Mapping and Profiling Suite Limb Profiler (OMPS-LP). To correct for this effect, we constructed NO2 climatology using simulated NO2 profiles with the GMI GEOS CCM model by averaging model data over 6 years. This climatology provides vertical NO2 profiles as a function of latitude, season, and local solar time. In this study, we evaluate the quality of the GMI climatology and compare it with the available measurements of NO2 profiles from SAGE III and Odin OSIRIS. We also evaluate sensitivity of the ozone retrieval algorithm to variations in stratospheric NO2.
OMPS-LP makes hyperspectral observations covering a spectral range from 295-1000 nm, but the coarse spectral resolution of LP hinders retrievals of NO2 profiles with traditional inverse models. Here we explore a new approach based on a machine learning (ML) algorithm to derive stratospheric NO2 vertical profiles from OMPS-LP. We train the ML algorithm using radiances calculated with the Gauss-Seidel limb scattering radiative transfer model and NO2 profiles derived from the GMI model. We evaluate NO2 profiles predicted by the ML algorithm and compare them with available measurements.

Speaker: Dr Jungbin Mok (SSAI)

11:20 Tracking ozone recovery with S-NPP OMPS Nadir and Limb profiler satellite and ground-based ozone records.

NOAA’s goal of understanding climate change is supported by operations of satellite and ground-based ozone observations that allow monitoring of atmospheric composition variability and long-term changes in the stratosphere and troposphere. Both satellite and ground-based (GB) observations are needed to track stratospheric ozone recovery and to evaluate the atmospheric radiative budget. Both GB and satellite observing systems rely on each other to assure the stability and consistency of collected records in time and space.
The NOAA long-term GB ozone records are collected by remote sensing and balloon-borne in-situ systems which are well-calibrated. Inter-instrumental homogenization of these long-term records is assessed through regular intercomparisons. The NESDIS Ozone Mapping and Profiler Suite (OMPS) instruments aboard the Suomi National Polar-orbiting Partnership (S-NPP) and Joint Polar Satellite System (JPSS) satellites collect global information about stratospheric ozone recovery. The NOAA Cohesive (COH) dataset combines OMPS and Solar Backscatter Ultraviolet Instrument (SBUV) data creating an over 40-year record of ozone data for use in trends and ozone monitoring. The stability of the OMPS measurements, both radiometric and in their Equator crossing times, their longer than "planned" lifetimes, and the reprocessing of the full records are key factors in their value as a component of the long-term satellite ozone record.
The S-NPP Limb profiler (LP) technique provides high vertically resolved profiles and therefore is of interest for analyses of atmospheric composition in the lower stratosphere (LS). The OMPS-LP data were used in two of the combined satellite records used in trend analyses (See Godin-Beekmann et al, 2022). Analyses indicate a continuous decline in LS ozone levels since 2000. The recent reprocessing of the Limb records by NASA addressed the drift in the S-NPP Limb records (Kramarova et al., 2022, AGU), thus creating an opportunity to repeat intercomparisons (presented in 2021) of the GB and OMPS satellite ozone records over an almost 10-year period. Implications of correction of the drifts in the S-NPP OMPS Limb ozone profiles on the derived stratospheric ozone trends will be discussed.

Speaker: irina Petropavlovskikh (CIRES and NOAA)

11:40 Impact of synoptic events on Arctic ozone using data from OMPS-LP, TROPOMI, and the MOSAiC ship campaign

Large-scale meteorologic events (e.g. cyclones), referred to as synoptic events, strongly influence weather predictability, but still cannot be fully characterized in the Arctic region because of the sparse coverage of measurements. Due to the fact that dynamics in the lower stratosphere and troposphere influences the ozone field, an approach to further analyze these events would be the use of space-borne measurements of ozone vertical distributions and total columns.

In this talk, we investigate the link between synoptic events and changes in the stratospheric ozone by using a combination of the unique measurements during the MOSAiC ship expedition, ozone profile and total column observations by satellite instruments (OMPS-LP, TROPOMI) and ERA-5 data. An approach to automatically identify and track cyclones using ozone observations will be discussed. By determining the altitude range where cyclones have the strongest influence on stratospheric ozone, we can define general conditions to best track cyclones with OMPS-LP ozone measurements.

Speaker: Falco Monsees

12:00 Hemispheric Asymmetry in Stratospheric Trace Gas Trends

Rising greenhouse gas emissions are changing the circulation in the stratosphere and subsequently altering the stratospheric composition. The result is that trace gas trends from the past two decades show a hemispheric asymmetry, with trends in each hemisphere having opposite signs. Here we discuss trends in observations from the limb instruments ACE-FTS and OSIRIS, as well as trends in model results from WACCM. N2O observations from ACE-FTS and simulations from WACCM are used as a proxy for stratospheric circulation in order to isolate the effects of chemistry on trends in O3, HCl, and NOy.

Speaker: Kimberlee Dube (University of Saskatchewan)

12:20 Ammonia (NH3) and solid ammonium nitrate in the upper troposphere: GLORIA airborne IR limb imaging measurements in the Asian Monsoon and in biomass burning plumes above the South Atlantic

We present trace gas and aerosol measurements obtained by the airborne infrared imaging limb sounder GLORIA (Gimballed Limb Observer for Radiance Imaging of the Atmosphere) that has been operated onboard the research aircraft Geophysica within the Asian Monsoon during the StratoClim campaign (July 2017) and onboard HALO (High Altitude and Long Range Research Aircraft) above the South Atlantic during the SouthTRAC campaign (September-November 2019). We show retrieval results of ammonia (NH$_3$) and solid ammonium nitrate (AN) as two-dimensional trace-gas distributions derived from GLORIA observations in the UT (Upper Troposphere). Retrieval performance and characteristics are discussed in detail. In this contribution, we further compare GLORIA measurements with results of the CAMS (Copernicus Atmosphere Monitoring Service) reanalysis and forecast model. The GLORIA observations reveal large enhancements of NH$_3$ of around 1 ppbv in the Asian Monsoon upper troposphere, but no clear indication of NH$_3$ in biomass burning plumes in the upper troposphere above the South Atlantic (instrument detection limit around 10 pptv). In contrast, CAMS reanalysis and forecast simulation results indicate strong enhancements of NH$_3$ in both measured scenarios. Comparisons of other retrieved pollution gases, such as peroxyacetyl nitrate (PAN) show the ability of CAMS models to reproduce the biomass burning plumes above the South Atlantic in general. However, NH$_3$ concentrations seem to be largely overestimated by the models within these plumes.

Speaker: Sören Johansson (Karlsruhe Institute of Technology)

12:40 Stratospheric Water Vapor Observations from the International Space Station by the Stratospheric Aerosol and Gas Experiment III (SAGE III/ISS)

The Stratospheric Aerosol and Gas Experiment III has routinely observed the upper atmosphere from the International Space Station (SAGE III/ISS) since June 2017. An important greenhouse gas and molecule affecting chemistry cycles, water vapor is among the vertical profiles of trace gases measured by SAGE III/ISS. This makes SAGE III/ISS the youngest of the current fleet of space-based instruments capable of measuring the vertical distribution of stratospheric water vapor (SWV). The SWV record is mature, a candidate for multi-instrument datasets, e.g. Stratospheric Water and Ozone Satellite Homogenized (SWOOSH) dataset, and shows promise within the GEOS Constituent Data Assimilation System. This presentation reviews the variations in SWV observed by SAGE III/ISS over the past half-decade. Variations highlighted include phase changes of the Quasi-biennial Oscillation (QBO), seasonal and monsoonal moisture patterns, and terrestrial events such as the recent January 2022 Hunga Tonga eruption that perturbed the SWV in spectacular fashion.

Speaker: David Flittner (NASA)

13:00 → 14:00 Lunch

17:30 → 22:00 Museum of Natural Sciences + dinner

Thursday, 25 May

09:00 → 09:10 Welcome and logistics

Speaker: Dr Noel Baker (BIRA-IASB)

09:10 → 10:10 Limb products validation

09:10 Recent Validation Results for the Atmospheric Chemistry Experiment (ACE)

In August 2023, the Canadian-led Atmospheric Chemistry Experiment (ACE) mission will complete its 20th year in orbit on board the SCISAT satellite. The long lifetime of ACE provides a valuable time series of composition measurements that contribute to our understanding of ozone recovery, climate change and pollutant emissions. The main instruments on board SCISAT use infrared and UV-visible spectroscopy to make their solar occultation measurements. The ACE Fourier Transform Spectrometer (ACE-FTS) is an infrared FTS operating between 750 and 4400 cm^-1 and the ACE-MAESTRO (Measurements of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation) is a dual UV-visible-NIR spectrophotometer which was designed to extend the ACE wavelength coverage to the 280-1030 nm spectral region. From these measurements, altitude profiles of atmospheric trace gas species, temperature and pressure are retrieved. The 650 km altitude, 74 degree circular orbit provides global measurement coverage with a focus on the Arctic and Antarctic regions. This paper will describe the validation results for the newest ACE-FTS and MAESTRO data sets

Speaker: Kaley Walker (University of Toronto)

09:30 The Stability of (Merged) Limb Ozone Profile Data Records used by ESA’s Climate Change Initiative

Since the mid-1980s, a series of limb and occultation instruments provide observations to assess past and recent changes in stratospheric ozone. Long-term changes are so small that the stability of the ozone profile climate data records (CDRs) must be better than ~2% per decade in order to be detected. Ensuring this level of stability poses a challenge for the teams providing datasets of individual sensors, for the teams combining these single-sensor data records into a multi-decade CDR, but also for the teams that quantify the stability of these records.

In support of the 2022 WMO/UNEP ozone assessment, we conducted a comprehensive analysis of the temporal stability of stratospheric ozone profile data sets from 17 limb and occultation satellite sensors and from the ozonesonde, stratospheric lidar and ground-based microwave radiometer measurement networks (NDACC, WMO GAW, SHADOZ). The considered satellite data records were acquired from the instrument teams, then screened and harmonised to common units and vertical grids by ESA’s Climate Change Initiative team. We present an update and extension of earlier analyses (Hubert et al., 2016) which contributed to the SPARC/IO3C/GAW LOTUS and the 2018 WMO/UNEP assessments. Such an update is timely since several satellite sensors (e.g., Aura MLS, OSIRIS, ACE-FTS) now operate years beyond their design life, often with reduced sampling capabilities and ageing detectors. Additional sensors are also included in the analysis (e.g., SABER, OMPS-LP, SAGE III/ISS) and revised versions of satellite data (e.g., OSIRIS, MIPAS, SCIAMACHY, Aura MLS) and ground-based datasets (e.g., ozonesonde). Since aggregated merged satellite records are used by most trend assessments, we extended our analysis of single profile data to monthly gridded profile data. This work was performed in direct support of the quality assessment of data records used and generated by ESA’s ozone CCI project and ECMWF’s C3S operational service.

We present updated estimates of the stability of single profile data (level-2) and of aggregated and merged profile data (level-3) from limb/occultation sensors relative to ground-based networks. The availability of comparison results for all sensors helps identify which satellite data records (or data versions) are the main cause of observed trend differences between merged satellite data records. This ensemble of comparisons also allows us to identify inhomogeneities in time and in space of the ground-based records, which, in turn, leads to a better understanding of the difference in trends between different ground-based techniques. Our work clearly demonstrates that simultaneous coherent analyses of multiple complementary satellite and ground-based data are a prerequisite to achieve the required level of stability for trend analysis. The transition to an era with fewer limb sensors will therefore challenge our ability to detect future ozone changes in a changing atmosphere.

Speaker: Daan Hubert (Royal Belgian Institute for Space Aeronomy (BIRA-IASB))

09:50 Validation of V8 MIPAS records of ozone and temperature

We report the results of validation exercise of ozone and temperature L2 MIPAS products, processed with IMK/IAA Level 2 scientific processor. Ozone profiles are compared to ACE-FTS, MLS, GOMOS, OSIRIS and SAGE II records, as well as to ozonesondes records from HEGIFTOM database.

Temperature profiles are compared to ACE-FTS, MLS and HALOE satellite records, GRUAN profiles, and COSMIC and CHAMP radiosondes records.

The exercise is refined by attributing a part of differences to the natural variability of ozone (or temperature), the natural variability fields calculated within TUNER initiative

Speaker: Alexandra Laeng (KIT, Germany)

10:10 → 10:30 ALTIUS

10:10 ALTIUS: Mission Scientific Objectives and Project Status

ALTIUS is a limb sounder mission that for the monitoring of the distribution and evolution of stratospheric ozone at high vertical resolution in support of operational services and long term trend monitoring. The ALTIUS mission will provide detailed stratospheric ozone profiles information at high vertical resolution, which adds valuable information to total column ozone used for data assimilation systems by operational centres based on nadir sounders. Secondary species, aerosol extinction profiles are temperature will be also provided.
The geophysical validation of the different ALTIUS products will provide also valuable scientific opportunities.
The ALTIUS mission is under implementation by ESA within the Earth Watch Program, with participation of Belgium, Canada, Luxembourg, and Romania.
Project is about to start it CDR, with an expected launch end of 2025.
The current Project status and plans covering flight model manufacturing, launch, commissioning, validation, and routine operations will presented.

Speakers: Daniel Navarro (ESA), Mr Michael François (ESA/ESTEC)

10:30 → 11:00 Coffee break

11:00 → 13:00 ALTIUS

11:00 ALTIUS operational ozone retrievals

ALTIUS is an original, groundbreaking mission which answers pressing questions and needs within the atmospheric remote sounding community. The project was proposed by the Belgian Institute for Space Aeronomy (BISA) and it is presently implemented as an element of the ESA Earth Watch program. The data processing algorithms will be developed in a collaboration between BISA, the University of Saskatchewan and the industry. Ozone and aerosol stratospheric profiles are the main operational objectives of the mission.
The truly innovative technology being developed through ALTIUS resides in the use of a high-performance microsatellite of the PROBA class that can operate in a multi-mode approach. Starting from a well-stabilized and controlled platform attitude, a single sensor can be optimized for a combination of limb scattering measurements and solar, stellar, and planetary occultations. The combination of an imager with an accurate attitude control allows for determining the tangent altitude by relating the instrument field of view to the satellite attitude.
We will present the baseline algorithm that will be implemented to retrieve the near-real-time operational ozone product.

Speaker: Didier Fussen (IASB)

11:20 The secondary scientific objectives of ALTIUS: additional species, approaches, and feasibility assessment

ALTIUS has been accepted as an Earth Watch mission with the primary objective of measuring concentration profiles of ozone in the stratosphere. But the mission has secondary scientific objectives which, however, are not driving the space segment developments. Recognizing that the instrumental concept of ALTIUS is offering opportunities for measuring at wavelengths relevant for other atmospheric species, and given the expected radiometric, spectroscopic, and pointing performances, a number of species have been identified as potential secondary targets of the mission. The development of the secondary products retrieval algorithms is starting, with the aim of having all the processing chains implemented in the payload data ground segment before the mission commissioning.
In this presentation, we will focus on the possibilities of the instrument itself, in particular the available spectral domain, and spectral resolution, and the radiometric performance. Based on these capabilities, a number of additional atmospheric species targets have been identified, with various levels of quality and confidence depending on the species themselves, and the observation modes. Algorithmic approaches to the retrieval of these species will be described, with a preliminary assessment of the feasibility.
The attention of the users and the validation communities will be drawn to the importance of expressing the needs well before the mission operation starts: the baseline acquisition scenarios of ALTIUS will not allow for retrieving all secondary species, and good identification of the needs in terms of seasons, locations, cadence, etc, will be important for maximizing the scientific return of the mission.

Speaker: Emmanuel Dekemper (BIRA-IASB)

11:40 In-flight Calibration of the ALTIUS Instrument

In-flight calibration techniques developed for ALTIUS at the University of Saskatchewan are presented. Simulated observations of the Sun, Moon and high-altitude atmosphere are used to measure instrument photo-response non-uniformity, spatial point spread function, wavelength registration and polarization response. The performance of the simulated techniques is assessed.

Speaker: Lorne Jensen (University of Saskatchewan)

12:00 Scintillation Mitigation Strategy and Validation of ALTIUS Stellar Occultation L2 Processor using GOMOS Observations.

ALTIUS (Atmospheric Limb Tracker for the Investigation of the Upcoming Stratosphere) is the upcoming stratospheric ozone monitoring mission of ESA’s Earth Watch program. ALTIUS consists of three 2D high resolution imagers: UV (250-355 nm), VIS (440-675 nm) and NIR (600-1040 nm) channels. Each channel is independent of the others and takes snapshots of the atmosphere in limb geometry at requested wavelengths. Stratospheric ozone profiles are the mission’s primary objectives. ALTIUS will measure in three different observation modes to maximize the spatial coverage of the mission: limb scattering on the dayside of the orbit, solar occultation at the terminator and stellar occultations on the nightside of the orbit.
In stellar occultation, the light coming from a star and passing through the atmosphere interacts with irregularities caused by turbulences and gravity waves. Therefore, the signal fluctuates along with the air density on the optical path. This phenomenon is called scintillation and can have a large detrimental effect on the measurements and on the retrieved profiles quality.
This work assesses the influence of scintillation on retrieved ozone profile and the performance of the mitigation strategy used in ALTIUS L2 processing algorithms in stellar occultation mode. Data originating from GOMOS (Global Ozone Monitoring by Occultation of Stars), an atmospheric sensor on board the ENVISAT satellite, is used to perform this study.

Speaker: Antonin Berthelot (BISA)

12:20 ALTIUS: System Characteristics and Performances

Based on highly autonomous and pointing-agile PROBA-NEXT Platform, the ALTIUS satellite embarks an optical instrument made of three independent channels (VIS, UV and NIR) to observe the Earth limb through a field of view of 100 km x 100 km, measuring scattered sun light (bright limb) and atmospheric attenuation (solar and stellar occultation mode) in fully tuneable monochromatic 2-D images.
The characteristics of the ALTIUS System, platform and instrument will be presented, together with the operational concept and the radiometric, spectral and geometrical performances at Level 1, as acquired by the instrument and corrected on ground.

Speakers: Daniel Navarro (ESA), Dr David Bühler (HE Space)

12:40 ALTIUS Geophysical Validation Plan

Programmed as an element of ESA’s Earth Watch programme, Atmospheric Limb Tracker for Investigation of the Upcoming Stratosphere (ALTIUS) has been developed as a gap filler mission responding to the urgent need to continue the global, long-term monitoring of stratospheric ozone, other trace gases and aerosols at the vertical resolution of the order of a few km. Scheduled for operation in the 2025-2029 period, ALTIUS will contribute near-real-time data to operational services like the Copernicus Atmosphere Monitoring Service (CAMS) and the Belgian Assimilation System of Chemical ObsErvations (BASCOE). ALTIUS will also provide consolidated data records to the Climate Data Store (CDS) of the Copernicus Climate Change Service (C3S) and to international assessments endorsed by the World Meteorological Organization (WMO) and the World Climate Research Programme (WCRP), as well as new research data needed for a better understanding of the upper atmosphere.

This contribution introduces the plan being developed for the geophysical validation of ALTIUS atmospheric composition data. After an overview of the user requirements against which ALTIUS data will have to be validated, the different objectives of ALTIUS validation during the commissioning phase of the mission and beyond will be discussed. The validation approach combines: (i) comparisons to independent ground-based measurements collected from monitoring networks contributing to WMO’s Global Atmosphere Watch (GAW), (ii) comparisons to other satellites like JPSS-2 OMPS and ACE extending the ground-based validation to the global domain, and (iii) quality assessments using modelling support. A dedicated validation service will perform baseline monitoring of ALTIUS data quality with an operational validation system, and in-depth validation producing consolidated results and support to the evolution of the retrieval algorithms. An Announcement of Opportunity for the calibration and validation (Cal/Val) of ALTIUS will be published approximately two years before launch, with the aim to open the ALTIUS Cal/Val to the international community and to a wider range of external data and activities, to foster exchanges within the validation community and with the instrument and algorithm experts, and to promote the use of ALTIUS data.

Speaker: Jean-Christopher Lambert (Royal Belgian Institute for Space Aeronomy (IASB-BIRA))

13:00 → 14:00 Lunch

14:00 → 14:40 Keynote talk: Limb scatter: techniques, algorithms, products

14:00 NASA Version 2.6 Ozone Profile Product from Suomi NPP OMPS Limb Profiler: summary of algorithmic changes and error analysis

The Limb Profiler (LP) is a part of the Ozone Mapping and Profiler Suite on the Suomi NPP satellite. We present a new version of the ozone profile product processed at NASA Goddard Space Flight Center (GSFC). In this study we summarize changes implemented in version 2.6 including changes in both Level 1 and Level 2 algorithms. In this presentation we focus on algorithmic Level 2 changes. The new retrieval algorithm (version 2.6) uses more wavelengths and combines measurements from UV and VIS parts of the spectra to retrieve a single vertical ozone profile between 12.5 km (or cloud tops) and 57.5 km. To improve ozone retrievals in the Upper Troposphere Lower Stratosphere (UTLS) region, we implemented a new aerosol correction that assumes a gamma-function particle size distribution. In addition, ozone and nitrogen dioxide cross sections and climatologies were updated. The main improvement in version 2.6 ozone product is the reduction in relative drifts between LP and correlative measurements, which were linked to a drift in the LP altitude registration. Finally, we discuss sensitivity of the ozone retrievals to implemented changes in Level 1 and Level 2 algorithms. We also provide an assessment of the total uncertainty budget.

Speaker: Dr Natalya Kramarova (NASA GSFC)

14:40 → 16:00 Limb scatter: techniques, algorithms, products

14:40 Combining Limb and Nadir Satellite Observations to Study Tropospheric Aerosols

Nadir near-UV measurements are used routinely to derive aerosol optical depth and single scattering albedo of desert dust and carbonaceous aerosols. Accurate retrieval of these parameters, however, requires aerosol layer height (ALH) information. Over dark vegetated-land and water surfaces, ALH can be retrieved using Oxygen A and B band observations from sensors equipped with those capabilities such as the S5P-TROPOMI and DSCOVR-EPIC instruments. However, in arid and semi-arid areas, the Oxygen-absorption-based methods do not work well to derive ALH because of large near-IR surface reflectance over these areas. Though the persistent presence of tropospheric clouds over most surface types makes the use of limb observations inoperable for tropospheric aerosols, limb observations can be used to derive the vertical distribution of tropospheric aerosols over the world’s largest deserts thanks to the low frequency of occurrence of tropospheric clouds over these regions. In this presentation we will describe a method for combining data from the OMPS nadir mapper (NM) and limb-profiler (LP) instruments on the NPP satellite to characterize the properties of tropospheric aerosols over the world’s arid and semi-arid regions.

Speaker: Dr Omar Torres (NASA Goddard Space Flight Center)

15:00 Direct inversion methods in limb scattering geometry

The processing of limb radiance observations is a difficult task due to the complexity of the forward model where several interfering species may interfere within multiple orders of scattering in the radiative transfer model. Furthermore, the observation geometry influences the observed radiance through the air masses, phase function and polarization.
In general, the inversion of limb radiances is performed by iterative methods due to the strong nonlinear character of the problem. The cost of the evaluation of the merit function is an important driver of the algorithm efficiency if many successive inversions have to be performed.
Here, we explore “direct” methods where a mapping is constructed between a large ensemble of limb radiance simulations and the set of atmospheric constituents used to produce them.
In the frame of the ALTIUS mission, we expect interferences between ozone and aerosol contributions depending on the atmospheric volcanic load. As an example of the power of direct methods, we address the issue of deriving aerosol properties and number density profiles.

Speaker: Dr Didier Fussen (IASB)

15:20 Retrieval of stratospheric aerosol extinction coefficients from OMPS-LP measurements

Stratospheric aerosols largely affect the radiative budget of the Earth’s atmosphere by scattering the incident solar radiation back to the space in the UV-Vis-NIR spectral range and by absorbing the radiation upwelling from the troposphere in the thermal infrared spectral range. Furthermore, stratospheric aerosols provide surface for heterogeneous reactions releasing halogenated compounds, which significantly contribute to the catalytic depletion of ozone, especially in the polar regions.
Despite its high scientific importance, the availability of information about the stratospheric aerosols on the global scale is quite limited. One of the widely used characteristics of the stratospheric aerosol, which is available from several space-borne instruments currently in operation, is the stratospheric aerosol extinction coefficient. Global vertical distributions of the stratospheric aerosol extinction coefficient with a dense spatial sampling are currently retrieved from measurements of the scattered solar light in limb viewing geometry (OSIRIS, SCIAMACHY, OMPS-LP) and from lidar measurements in nadir viewing geometry (CALIPSO). The retrievals from solar occultation measurements (SAGE II, SAGE III) are most robust and suitable for usage as a validation source, they suffer, however, from a lack of spatial sampling and coverage.
The main challenges in the retrievals of the aerosol extinction coefficient from limb-scatter measurements are a lack of information about aerosols at higher altitudes, correlation of the aerosol scattering signal and surface albedo reflection and a lack of information about aerosol particle size distribution. Several retrievals currently exist, which try to minimize the influence of some of these uncertainty components. In this study we present a new retrieval of the aerosol extinction coefficient developed at the University of Bremen, which is focused on minimizing the effect of unknown aerosol loading at high altitudes. This is especially crucial in the case of volcanic eruptions reaching high altitudes, such as that of Hunga Tonga - Hunga Haʻapai in January 2022. The retrieval algorithm details will be discussed in the presentation and the obtained results will be compared with those from other satellite instruments (OSIRIS, SAGE III/ISS).

Speaker: Alexei Rozanov (Institute of Environmental Physics, University of Bremen)

15:40 The Aerosol Limb Imager: Multi-Spectral Polarimetric Observations of Aerosol and Cloud

The Aerosol Limb Imager (ALI) is a multi-spectral polarimetric imager designed to observe scattered sun light in the limb. ALI collects images in a narrow spectral band in one of two orthogonal polarization states for the purpose of retrieving aerosol number density and particle size information within the upper-troposphere lower-stratosphere. Of novelty is the polarimetric nature of the aerosol observations. The two orthogonal polarization states are used to detect cloud in the spectral data and facilitate its distinction from aerosol.
To obtain an image at a desired wavelength and polarization state, ALI employs a system of linear polarizers, a liquid crystal rotator, and an acoustic-optic tunable filter. These components use no moving parts and provide the capability of imaging in the two polarizations at a select wavelength between 500 nm and 1500 nm.
To date, multiple iterations of the ALI instrument concept have been demonstrated on stratospheric balloon platforms. The current version of ALI has been successfully deployed on two separate stratospheric balloon launches: 2021 in Kiruna, Sweden and 2022 in Timmins, Ontario. From the geometry afforded by a stratospheric balloon, ALI can provide a spectral sample in increments of <100 meters and produces useful aerosol observations between 9 km and 30 km in altitude.

Speaker: Daniel Letros (University of Saskatchewan)

16:00 → 16:30 Coffee break

16:30 → 17:10 Limb scatter: techniques, algorithms, products

16:30 Investigating the effects of inhomogenieties in surface reflectivity on stratospheric ozone retrievals from limb scattering observations

Retrieval artifacts from 1D limb retrievals, which assume homogeneous atmospheric properties along the satellite line of sight (LOS), are known but generally associated with variations in the trace gas concentration or temperature. The focus of this study is the investigation of a retrieval artifact identified in tropospheric ozone data and ozone limb profiles retrieved from OMPS-LP observations at the University of Bremen (IUP) which is associated with an inhomogeniety in the surface reflectivity.

At the IUP, a tropospheric ozone column (TrOC) product has been produced by exploiting the limb-nadir matching technique applied to OMPS observations. Looking at yearly averaged maps of this TrOC data set, we noticed an artifact in the tropical Pacific region, i.e. higher ozone columns in the [0°N, 5°N] latitude band, a region where the tropospheric ozone is expected to be fairly homogeneous. This issue was traced back to the stratospheric profiles, which show a lower ozone content at their peak altitude. By applying the limb-nadir matching technique, this artifact propagates into the TrOC data. This feature is also visible in the Atlantic, though less pronounced, and exceeds the typical uncertainty of the TrOC, being of the order of 5-7 DU.

This artifact has been associated with the semi-permanent presence of the Inter-Tropical Convergence Zone (ITCZ), which constitutes a region of high reflectivity across the satellite LOS. It has been identified in other stratospheric ozone column (SOC) and TrOC data sets, e.g. the NASA OMPS product, SCIAMACHY TrOC and also in the USask OMPS stratospheric ozone, despite the applied tomographic approach. Evidences of the link between the presence of a high reflectivity cloud band pattern over the tropical Pacific and the artifact in ozone profiles and SOCs are shown . This is done by classifying ozone profiles as a function of distance between the respective TP and high reflectivity pixels from OMPS nadir data.

The final aim of this study is the improvement of the TrOC product derived from satellite limb scattering measurements. Further studies are required with the goal to implement in the radiative transfer model (RTM) SCIATRAN at the University of Bremen the possibility of taking into account variations of the surface reflectivity along the satellite LOS. The outcome could be of interest for any limb scattering instrument, e.g. SCIAMACHY and ALTIUS.

Speaker: Carlo Arosio (Institute of Environmental Physics, University of Bremen)

16:50 Applying neural network methods to Suomi NPP OMPS LP measurements

In this study we demonstrate how neural network (NN) models can be used to improve our understanding of OMPS LP measurements, optimize forward modeling, and enhance OMPS LP retrievals. Retrieving atmospheric profiles from limb observations requires modeling how solar light scatters through the atmosphere. Operational retrieval codes make approximations for computationally expensive processes like multiple scattering (MS) to enable their application to large volumes of measurements. In recent years, machine learning techniques such NNs have been demonstrated to significantly reduce the computational time of modeling methods. Here we present an alternative MS approximation method for limb simulations based on NNs. We also demonstrate an alternative NN retrieval algorithm for inverse problems where traditional methods fail, like retrieving NO2 from OMPS LP. We discuss the optimal training strategies for the NNs as well as the accuracies of the trained models.

Speaker: Michael Himes (NASA Postdoctoral Program Fellow, NASA Goddard Space Flight Center)

17:10 → 17:30 Occultation: techniques, algorithms, products

17:10 Minor species in the Venus mesosphere from SOIR on board Venus Express

We report on the detection and upper-limit of SO$_2$, SO$_3$, OCS, H$_2$S, CS, H$_2$CO, O$_3$, NH$_3$, HCN, N$_2$O, NO$_2$, and HO$_2$ above the cloud deck using the SOIR instrument on-board Venus Express [1, 2].

The SOIR instrument [3] performed solar occultation measurements in the IR region (2.2 - 4.3 µm) at a spectral resolution of 0.12 cm$^{-1}$, among the highest of all space instruments. It combined an echelle spectrometer and an Acousto-Optical Tunable Filter for the order selection. SOIR performed more than 1500 solar occultation measurements leading to about two millions spectra [4].

The wavelength range probed by SOIR allows a detailed chemical inventory of the Venus mesosphere, above 60km, at the terminator with an emphasis on vertical distribution of the gases.

In this work, we report detections of minor species poorly constrained so far in the Venusian mesosphere. The implications of these detections for the chemistry will be addressed, as will possible cross-correlations between different species.

References:
[1] Mahieux, A., et al. (2023), Icarus, Under review.
[2] Mahieux, A., et al. (2023), Icarus, In preparation.
[3] Mahieux, A., et al. (2008), Applied Optics, 47.
[4] Vandaele , A.C., et al. (2016), Adv. Space Res., 57.

Speaker: Arnaud Mahieux (IASB/BIRA)

17:30 → 19:30 Poster session #2

17:30 Advantages of the synergy between limb and nadir observations: 2D data fusion of CAIRT, IASI-NG and Sentinel 5 simulated data

The Changing-Atmosphere Infra-Red Tomography Explorer (CAIRT) is one of the four candidates for ESA’s Earth Explorer 11. By exploiting its imaging capabilities, CAIRT can sound the atmosphere simultaneously from the middle troposphere to the lower thermosphere at high spectral resolution and with unprecedented horizontal and vertical resolution. Flying in loose formation with MetOp-SG mission allows to combine spatially resolved limb observations with horizontally resolved nadir measurements of IASI-NG and Sentinel-5 nadir spectrometers to extend limb observations down to the surface. We have evaluated further possible advantages coming from the exploitation of the synergy between limb and nadir imaging observations for Ozone in 2D, i.e. with the analysis performed both in the vertical direction and in the along track direction. The synergistic products are characterised on one hand by a better quality in the troposphere than the one of nadir only measurements, thanks to the limb measurement knowledge on the vertically resolved stratosphere, on the other hand also by a better quality in the Upper Troposphere - Lower Stratosphere than the one of limb observations only, thanks to the nadir measurements knowledge on the horizontal variability of the atmosphere in the troposphere. We will show results obtained with the rigorous approach of 2D complete data fusion for realistic simulations of CAIRT, IASI-NG and Sentinel 5 observations.

Speaker: Piera Raspollini (IFAC-CNR)

17:30 Dust climatology from NOMAD UVIS channel

Aerosols are present in the atmosphere of Mars and have a major effect on it. They are mainly composed of dust, water ice and CO2 ice. Dust is confined to lower altitudes during the aphelion season and can reach higher altitudes during the perihelion, especially during dust storms that frequently arise on Mars. These storms can sometimes grow up to cover the entire planet and are then called global dust storms. They have important consequences on the atmosphere as dust will heat the atmosphere and change its composition.
The NOMAD (“Nadir and Occultation for MArs Discovery”) spectrometer suite onboard the ExoMars Trace Gas Orbiter (TGO) is composed of three spectrometers. In this work, we will use the UVIS channel in occultation mode. With this channel we will derive the size of the particle and study the climatology.
Using only the spectral range of UVIS, the dust, water ice and CO2 ice cannot be differentiated because the three aerosols have similar spectral features in the UV-visible. However, it is possible to distinguish the particle size. Dust represents the majority of the aerosols present in the atmosphere, therefore only dust will be assumed in this work. Detection of CO2 and water ice will be investigated in a future work
We observe three different spectral features characteristic of dust in the UV. Large particles above 1.2 micron show a relatively flat spectra, while oscillations seem to characterize the medium particles between 0.5 and 1 micron, particles smaller than 0.5 micron are characterized by a spectral slope.
Knowing the size of the grain, the vertical profile are key elements to understanding its radiative property. The result will also show the climatology of the dust and several vertical profiles.

Speaker: zachary Flimon (BIRA-IASB)

17:30 Examples of Applying Machine Learning to Observations of the Aura Microwave Limb Sounder

The data record of the Aura Microwave Limb Sounder (MLS) currently covers more than 18 years, far exceeding its original 5-year design life. As part of the A-train constellation, the long MLS data record and the comparatively high spatio-temporal resolution of its retrieval products provide a unique opportunity to apply machine learning techniques to enhance its observational capabilities.

This talk presents four particular examples where artificial neural networks (ANNs) were trained on MLS observations to reliably predict a variety of different atmospheric properties: (i) cloudiness and cloud top pressure in the vicinity of individual MLS profiles, (ii) more accurate near-real-time profiles of atmospheric properties and constituents, (iii) methane and chlorine nitrate profiles at the MLS spatial and temporal resolution, and (iv) the bias in MLS 100-hPa geopotential height with respect to MERRA2.

Speaker: Frank Werner (Jet Propulsion Laboratory, California Institute of Technology)

17:30 First studies on CAIRT's capabilities to deduce spatial structures and gravity wave momentum flux

The Changing-Atmosphere Infra-Red Tomography Explorer (CAIRT) is one of four candidates for ESA’s Earth Explorer 11. It's imaging capabilities will be used to offer several independent measurement tracks across its swath and thus deliver, in combination with tomographic retrieval techniques, a true 3-D product with a high vertical resolution (down to 1km).

In this work, we will examine and showcase the 3-D spatial resolving capabilities of the instrument by describing the employed algorithms and the examining the 3-D resolution of the temperature product and selected trace gasses. Selected fields derived from non-linear and tomographic end-to-end simulations will be shown.

Gravity waves are essential drivers of the middle atmosphere circulation through drag deposited by their breaking and saturation. The 3-D capability of CAIRT allows to reproduce the spatial structure of gravity waves and thus a full quantification of orientation, direction, and amplitude. These parameters enable the computation of gravity wave momentum flux. An in depth study was performed to examine how well the gravity wave momentum flux present in NWP data, here assumed as truth, can be reproduced by simulated CAIRT observations. We will present the study design and the results.

Speaker: Jörn Ungermann (Forschungszentrum Jülich GmbH)

17:30 GOMOS-AerGOM: Recent and current activities for C3S, CAMS and SPARC

AerGOM is a retrieval algorithm that was specifically designed to retrieve stratospheric aerosol extinction from the Global Ozone Monitoring by the Occultation of Stars (GOMOS) experiment that was launched onboard Envisat and provided measurements of the Earth atmospheric limb between 2002 and 2012.

While AerGOM retrieves simultaneously aerosol extinction, ozone, nitrogen dioxide and nitrogen trioxide for every night-time occultation measurements (Level 2), the resulting dataset of aerosol extinction is used to produce gridded aerosol datasets (Level 3) with a 5-day time resolution, 5-degree latitude resolution and 60-degree longitude resolution. This dataset, distributed in the framework of the Copernicus Climate Change Service (C3S) and referenced as C3S-GOMOS, can be used for modelling applications, and two such applications are presented in this communication.

The first one is the use of C3S-GOMOS (V. 4.00), to contribute to the reconstruction of a comprehensive inventory of spatially resolved sulfur injections by volcanic eruptions based on the EMAC chemistry-climate model (EMAC5/MESSy Atmospheric chemistry).

More recently, C3S-GOMOS (V. 4.00) has been used for the validation of the Integrated Forecasting System (IFS) of the Copernicus Atmospheric Monitoring Service (CAMS), and more particularly the stratospheric extension of the IFS-AER model, which is the scope of the current CAMS2_35 project.

This communication will present the latest news about the development of AerGOM and C3S-GOMOS, as well as an overview of these two model-related applications.

Speaker: Christine Bingen (BIRA-IASB, Brussels, Belgium)

17:30 Lyman-alpha Solar Occultations of the Earth’s Geocorona Using GOES-R

The Earth’s hydrogen (H) corona has been observed from various platforms for over half a century and many of these measurements, particularly those made in recent times, leverage the observation of solar H-Lyman-α (121.6 nm) photons resonantly scattered by H. Interpreting these observations becomes increasingly complex in the optically thick region of the corona below 3 Earth-radii (RE) where the one-to-one correspondence between observed photons and scattering atoms breaks down due to multiple scattering effects. Solar occultation provides an alternative approach to observing the H corona in both the optically thin and thick regimes. In particular, solar occultation leverages absorption spectroscopy which is inherently less sensitive to multiple scattering effects allowing for direct observations of H density below 3 RE, albeit with its own set of complexities, assumptions and limitations.
In this study, we use new measurements of solar H-Lyman-α from the EUV and X-ray Irradiance Sensors (EXIS) aboard the Geostationary Operational Environmental Satellite (GOES) -R series satellites to measure H from 1.2 to 5 RE. The retrieval approach and its random uncertainty and systematic error in both the optically thin and optically thick regime are presented. Observations are compared with existing data and models.

Speaker: Ed Thiemann (LASP, University of Colorado)

17:30 Modelling aerosols in Jupiter’s atmosphere with ASIMUT-ALVL

The study of Jupiter’s atmosphere is of interest to the scientific community, including its composition, evolution, distribution, structure, and dynamics around the planet. Although the main chemical composition of Jupiter’s atmosphere has been unraveled, many questions remain open, such as the global abundance of water, or the responsible chemistry for the coloration of the clouds. ASIMUT-ALVL, a Radiative Transfer (RT) code developed at the Royal Belgian Institute for Space Aeronomy (BIRA-IASB), has been recently upgraded to include the study of Jupiter’s atmosphere. Within the main contributions observable in the VIS-NIR spectrum of Jupiter’s atmosphere, it was necessary to apply the current knowledge of the physical and chemical characteristics of Jupiter, including the Rayleigh scattering contribution due to dominant atmospheric species, the refractive index of Jupiter’s atmosphere, the Collision-Induced Absorption (CIA) due to H$_2$-H$_2$ and H$_2$-He molecular systems, the typical temperature profile and atmospheric composition (from Moses et al. 2005), and the required line-lists from the HITRAN online database with line parameters adequate for an H$_2$ and He dominant atmosphere (following the 2020 version release). To model the aerosols and hazes present in the atmosphere, including the chromophores, the microphysical parameters were obtained as described by Lopez-Puertas et al., 2018, and Baines et al., 2019. The model was finally validated after reproducing VIMS/Cassini observations obtained during the flyby to Jupiter. The upgraded version of ASIMUT-ALVL is supporting the assessment of the capabilities of the Moons And Jupiter Imaging Spectrometer (MAJIS), one of the key scientific instruments on board the Jupiter Icy Moons Explorer (JUICE), the next mission to the Jovian system from the European Space Agency (ESA), to be launched in April 2023 with an arrival date on July 2031. MAJIS will provide hyperspectral capabilities through two channels: VIS-NIR (0.5μm-2.35μm), and IR (2.25μm-5.54μm), with a remarkable potential of VIS-NIR spectrometry for characterizing the vertical structure and composition of Jupiter’s atmosphere.

Speaker: Miriam Estefanía Cisneros González (Royal Belgian Institute for Space Aeronomie)

17:30 Moon occultation measurements simulation and retrieval with ALTIUS

To monitor stratospheric ozone and aerosols, the ALTIUS mission will perform measurements either in limb scattering mode or in occultation mode. In this mode, the satellite will observe the Sun during sunrise and sunset, and the rises and sets of the brightest stars and planets during the night. To increase the geographic coverage of the observations, lunar measurements will also be carried out, when the spacecraft is in the Earth shadow. The variable shape and brightness of the Moon, however, make the simulation and the retrieval works difficult. This poster describes how the lunar mode has been processed in the scene generator created to simulate the ALTIUS observations, as well as how the ALTIUS Moon images will be used to retrieve ozone vertical profiles.

Speaker: Philippe Demoulin (Royal Belgian Institute for Space Aeronomy)

17:30 Performance of an ozone retrieval algorithm using direct calls to a Monte-Carlo RTM for the limb-scatter mode of ALTIUS.

ALTIUS (Atmospheric Limb Tracker for the Investigation of the Upcoming Stratosphere) is the upcoming stratospheric ozone monitoring mission of ESA’s Earth Watch program. ALTIUS consists of three 2D high resolution imagers: UV (250-355 nm), VIS (440-675 nm) and NIR (600-1040 nm) channels. Each channel is independent of the others and takes snapshots of the atmosphere in limb geometry at requested wavelengths. Stratospheric ozone profiles are the mission’s primary objectives. ALTIUS will measure in three different observation modes to maximize the spatial coverage: limb scattering on the dayside of the orbit, solar occultation at the terminator and stellar occultations on the nightside of the orbit.
The forward model used for the limb scattering L2 processing chain is a neural network trained on a large set of radiance profiles computed by a Monte-Carlo Radiative Transfer Model (RTM) called Smart-G. This approach is an attempt to make the retrieval algorithm benefit from the accuracy of a Monte-Carlo model, while circumventing the large computation load. While the neural network used as a proxy for Smart-G is orders of magnitude faster than a Smart-G simulation and provides good accuracy, it also comes with limitations in the number of state vector elements that can be used.
In this work, a parallel retrieval algorithm was built to explore the high-resolution capabilities of ALTIUS. In this retrieval algorithm, the forward model is Smart-G itself without the use of a proxy. Good Ozone retrieval performance is achieved on simulations and the vertical resolution of ALTIUS is assessed. Challenges caused by the use of a non-deterministic model (i.e. Monte Carlo) are discussed.

Speaker: Antonin Berthelot (BISA)

17:30 Quantifying the Drift and Biases of Ozone Mapping and Profiler Suite Limb Profiler (OMPS-LP) v2.6

Using ozonesonde data from the Harmonization and Evaluation of Ground Based Instruments for Free Tropospheric Ozone Measurements (HEGIFTOM) and other satellite data sets (e.g. MLS), we compared the ozone trend from Ozone Mapping and Profiler Suite Limb Profiler (OMPS-LP) in upper troposphere and lower stratosphere (UTLS). The detailed comparisons between these datasets reveal the temporal and altitude- and latitude-dependent bias and drift of OMPS-LP version 2.6 data, which shows the improvement of the data quality of OMPS-LP v2.6 compared to previous version. The bias and drift suggest the necessity to revisit the ozone trend by OMPS-LP, which will also improve the quality of homogenized datasets with OMPS-LP incorporated (e.g. SWOOSH) through bias and drift characterization and correction.

Speaker: Yue Jia

17:30 SAGE III/ISS Version 5.3 Data Product Improvements Using a Disturbance Monitoring Package

The Stratospheric Aerosol and Gas Experiment III (SAGE III) is an externally affixed payload on the International Space Station (ISS; SAGE III/ISS). SAGE III/ISS retrieves highly resolved vertical profiles of gaseous atmospheric constituent number density including ozone, water vapor, and nitrogen dioxide, as well as aerosol extinction coefficient at nine wavelengths in the visible to near-IR spectrum. Retrievals can be performed using the primary solar occultation mode as well as lunar occultation and limb scattering modes. The SAGE III/ISS retrieval algorithm utilizes the combination of a high signal-to-noise ratio granted by native retrieval of solar transmission during solar occultation and accurate pointing knowledge from using the Sun as a celestial reference to calibrate in-atmosphere observations against the sampled exoatmospheric reference. However, ISS presents additional challenges as a dynamic platform that performs frequent attitude maneuvers, has visiting vehicles, changes configurations, and produces a unique vibration environment which is unusual relative to typical three-axis stabilized satellite platforms frequently employed by remote sensing measurements. These disturbance events can add small but noticeable amounts of error ranging from small alignment errors in the attachment stack mounting the payload to ISS to variations in bending modes experienced by ISS given SAGE III/ISS’s location at S3 on the starboard truss. These pointing errors introduce additional uncertainty by muddling geolocation and altitude attribution as well as during the association of in-atmosphere packets against matched exoatmospheric samples on the solar disk. The 5.3 release of the SAGE III/ISS data product utilizes the Disturbance Monitoring Package (DMP) subsystem to monitor changes to payload attitude at the SAGE III/ISS mounting location not reported in the ISS attitude product. For this release the DMP pointing corrections have been applied to the solar occultation product. The DMP is a Miniature Inertial Measurement Unit (MIMU) developed by Honeywell Aerospace consisting of three orthogonally block-mounted Ring Laser Gyros (RLGs). The DMP measures rotations in three orthogonal directions in inertial space in contrast to the effective yaw and pitch provided by the SAGE III/ISS scanhead’s azimuth and elevation controls. Rotation, or disturbance, are reported at 200 Hz and resolved to 1 µrad. Incorporation of DMP data has drastically improved pointing knowledge in the retrieval error and allowed for the identification and correction of mechanical disturbances that may occur during events. Improvements have been observed in vertical profiles of atmospheric transmission in both undisturbed (quiescent) events and high-disturbance environments. Up to 10% of solar occultation events were noted to have experienced high levels of disturbance, and a median reduction of up to 30% in just the AO3 ozone number density product uncertainty was observed for all events processed using the DMP correction. This presentation will highlight the improvements observed for all retrieved SAGE III/ISS data products. Applicability to platforms beyond environments such as ISS as well as relative pointing techniques such as limb scattering will also be discussed.

Speaker: Kevin Leavor (Science Systems and Applications, Inc.)

17:30 Simulation based advancement in polar stratospheric cloud detection and classification for the satellite based infrared limb sounder Envisat MIPAS

Polar stratospheric clouds (PSC) play an important role in polar ozone loss. However, there are still gaps in our knowledge about PSCs and nitric acid trihydrate (NAT) particles in particular. Active lidar and passive limb emission satellite instruments allow for PSC measurements over the entire winter season at both poles and provide a classification between the three types: ice, NAT, and supercooled ternary solutions (STS).

NAT PSCs cause a specific spectral signature at around 820 cm-1 in infrared limb emission spectra. However, it turned out that the spectral signature varies: from a distinct peak with a maximum at 820 cm-1, to a shifted peak with a maximum at smaller wavenumbers to a broader step-like feature between 810 to 830 cm-1. Reasons for the shift may be the shape of the particles and the particle size.

In our study, we focused on Envisat MIPAS measurements and simulated ice, NAT, and STS particles. The simulations cover a comprehensive parameter range of particle sizes and number densities/extinctions as well as numerous cloud altitudes and thicknesses. Based on the simulations we improved the PSC detection and classification capabilities by deriving new separation thresholds. From the simulated NAT/ice/STS scenarios 98/98/97% could be unambiguously identified as NAT/ice/non-ice PSCs, respectively. The remaining scenarios fall into the category of "unknown".

For NAT PSCs our simulations show that the observed shift of the spectral feature is sensitive to particle size. Hence, we derived a coarse NAT particle size classification scheme for small (S<=1.µm), medium (M=1.5-3.5µm), and large (L=4-8µm) NAT particles based on the different shapes of the spectral feature. From the simulated NAT scenarios, 94/96/94% were classified correctly as S/M/L NAT, respectively.

Finally, we applied the improved PSC detection and classification algorithm as well as the new NAT size classification to the 10 years of MIPAS measurements. The number of NAT detections increased compared to previous analyses because the new method is sensitive to NAT particles larger than 3µm, which the previous method was not. In the Antarctic small NAT particles dominate and the number of NAT detections increased by a factor of about 1.2. In the Arctic medium and large NAT particles dominate and the number of NAT detections increased by a factor of about 2.

Speaker: Sabine Griessbach (Forschungszentrum Jülich)

17:30 Stratospheric aerosol size decrease after volcanic eruptions

The evolution of the size distribution of stratospheric aerosols after volcanic eruptions is still not understood very well, due to the temporal sparsity of in situ measurements, the low spatial coverage by ground based observations and the difficulties to derive aerosol size information from satellite measurements. To contribute to this ongoing research, we show data from our aerosol size retrieval using SAGE III/ISS solar occultation measurements. Using a three wavelength extinction approach the parameters of assumed to be monomodal lognormal particle size distributions are retrieved.

Surprisingly we find that some volcanic eruptions can lead to a decrease in average stratospheric aerosol size, in this case the eruptions of Ambae in 2018, Ulawun in 2019 and La Soufrière in 2021, while other eruptions have a more expected increasing effect on the average particle size, like the 2019 Raikoke eruption. We show how different parameters like the median radius, the absolute mode width and the number density evolve after the mentioned eruptions.

Additionally, as a part of our ongoing research to understand the underlying mechanisms controlling the observed aerosol size reduction, we show simulations of the aforementioned volcanic eruptions using the aerosol-climate model MAECHAM5-HAM. Although the initial conditions in the model simulations are different from observations due to missing smaller emissions in the time before the eruptions, a good agreement in the perturbations of the extinction coefficient was achieved.

Speaker: Felix Wrana

17:30 The Aerosol Limb Imager: Modelling Measurements of a Geoengineering Plume

Solar radiation management has been proposed as a method to combat and control changes in the climate of Earth. The method aims at the intentional releasing of aerosol into the atmosphere to adjust radiative forcing. However, there is significant uncertainty in the evolution of artificial aerosol particles, as well as the atmospheric dynamics of such a release. The Stratospheric Controlled Perturbation Experiment (SCoPEx), lead by the Harvard School of Engineering and Applied Sciences, wishes to study solar radiation management with the goal of reducing the uncertainty of such an exercise.
The SCoPEx project has done significant work on modelling the evolution of artificial aerosol particles as they would be released from a stratospheric balloon. To complement this, the SCoPEx project purposes a localized experiment, in which a small amount of aerosol is released from such a balloon, to validate and advance the understanding.
The Aerosol Limb Imager (ALI) is a multi-spectral polarimetric imager. ALI is designed for operation on a stratospheric balloon platform and takes images of limb scattered sunlight at two orthogonal polarization states. ALI images produce spectral measurements between 500 nm and 1500 nm with a tangential altitude resolution of < 100 meters.
The observational technique of ALI allows it to serve as an ideal measurement tool for an experiment such as that purposed by SCoPEx. In pursuit of this endeavour, modelling has been done to simulate ALI observations of localized aerosol plumes in efforts to determine the extent of information limb measurements can yield.

Speaker: Daniel Letros (University of Saskatchewan)

17:30 The ALTIUS Bright Limb Aerosol Retrieval Algorithm: Current Status and Future Developments

The Atmospheric Limb Tracker for the Investigation of the Upcoming Stratosphere (ALTIUS) is a high spatial resolution spectral imager designed to measure ozone and other trace species in the stratosphere. A stratospheric aerosol retrieval is included to provide input for the ozone retrieval, and an official stratospheric aerosol secondary product is expected. Here we describe the stratospheric aerosol retrieval algorithm used in bright limb mode, planned modifications for the official secondary product, and expected performance . A standard optimal estimation scheme is used with Tikhonov regularization to constrain the profile. The stratospheric aerosol secondary product retrieval will be based upon the OSIRIS v7 multi-wavelength aerosol retrieval (Rieger, et al. 2019, https://doi.org/10.1029/2018JD029897). We also present the current status of the performance of the algorithm using simulated retrievals with a full instrument model, as well as optimizations that are being made to improve the convergence of the algorithm

Speaker: Bion Larson

Larson_Limb_Workshop_2023.pptx

17:30 The Radiative Transfer Model used in the bright limb retrieval of the ALTIUS project

We give an overview of the Radiative Transfer Model (RTM) used in the bright limb retrieval of the ALTIUS project.
The chosen RTM is SMART-G, which is an RTM of Monte Carlo type, owned by HYGEOS, Euratechnologies, 165 Avenue de Bretagne, 59000 Lille, France, Tel: + 33 (0) 3 20 08 24 98, E-mail: contact@hygeos.com.

SMART-G is BISA's preferred Radiative Transfer (RT) software tool for the ALTIUS project. SMART-G serves as the core of the forward model, used in the L2 processing chain for the ALTIUS data stream.

SMART-G is a state-of-the-art RTM, which computes Stokes vector fields in a spherical shell atmosphere. It includes polarisation, refraction, multiple Rayleigh scattering, absorption by gases and scattering and absorption by aerosols, having arbitrary Mueller matrix phase functions. It also supports non-homogeneous, spectral and polarising Earth albedo models.

SMART-G runs on Nvidia GPUs. It is written partly in Python and partly in CUDA C. It is installed at BISA on several dedicated Linux machine with industrial quality, high performance GPUs.

SMART-G is driven by the "ALTIUS Interface to SMART-G", a collection of 30 python modules developed at BISA, which provides RT support for the ALTIUS project. This is a very general and user friendly tool, which frees the user from having to deal with the specific details of how to set up the input structures for and how to call SMART-G. The Interface main features will be introduced.

Speaker: Ghislain Franssens

Friday, 26 May

09:00 → 09:10 Welcome and logistics

Speaker: Dr Noel Baker (BIRA-IASB)

09:10 → 09:50 Keynote talk: Aerosol and clouds: profiles, composition, trends

09:10 Particle Size Distribution Parameters from SAGE III/ISS Extinction Spectra, with Application to the 2022 Hunga Tonga Eruption

Stratospheric aerosols play key roles in the chemistry and radiation balance of the atmosphere and are a key input parameter for global chemistry and climate models. The degree to which aerosols impact chemistry and radiation balance depends primarily on the relative abundance of different sized particles within the sample volume, often referred to as the particle size distribution (PSD). If the PSD is accurately known then other key modeling parameters (e.g., surface area density and effective radius) can be derived. Historically, occultation observations from orbital instruments such as SAGE III/ISS have been used to infer these PSD parameters by inverting the extinction coefficient spectra. However, past efforts routinely failed to account for measurement uncertainty and lacked a rigorous estimate of the inferred PSD uncertainty. We carried out a series of simulations to evaluate the accuracy of these inferences and, for every valid SAGE III/ISS extinction spectrum, determined the range of PSD parameters that fell withing the bounds of the extinction error bars. Special application of this method was applied to estimate the impact of the 2022 Hunga Tonga eruption had on particle size distributions.

Speaker: Dr Travis Knepp (NASA LaRC)

09:50 → 10:30 Aerosol and clouds: profiles, composition, trends

09:50 Measurements of the 2022 Hunga Tonga-Hunga Ha'apai Aerosol Cloud Using Space-Based Observations

On 15 January 2022, the submarine Hunga Tonga-Hunga Ha'apai volcanic eruption lofted materials high into the upper stratosphere, reaching a record-breaking altitude of ~58 km, unprecedented in the satellite observations era. Within two weeks, the bulk of the injected material circulated the globe between 20 – 30 km altitude, as observed by the OMPS LP instrument. Initial predictions suggested that the direct impact on Earth's radiation budget may not be as significant as the 1991 Pinatubo eruption because of the relatively low sulfur dioxide (SO2) injection, estimated to be 0.4 Tg compared to the 20 Tg from Pinatubo. We estimated however that the stratospheric aerosol optical depth (sAOD) measured by OMPS LP is the largest since the Pinatubo eruption and is at least twice as great as the sAOD after the 2015 Calbubo eruption despite the similar SO2 injection from that eruption.
We use space-based observations of OMPS LP, SAGE III/ISS, and CALIPSO to monitor the Hunga-Tonga volcanic plume evolution and transport at different altitudes as it circulates the globe. While the main aerosol layer initially remained trapped in the tropical pipe, significant parts of the aerosol layer were transported to the south pole and played a significant role in this year’s large ozone hole.

Speaker: Dr Ghassan Taha (MSU/NASA GSFC)

10:10 Tomographic retrievals of Hunga Tonga-Hunga Ha’apai volcanic aerosol

The 2022 eruption of the Hunga Tonga-Hunga Ha’apai volcano caused substantial impacts on the atmosphere, including a large increase of stratospheric aerosol at high altitudes and a massive injection of water vapor. We show results from application of a two-dimensional tomographic retrieval of aerosol extinction profiles from limb scattered sunlight made by the NASA OMPS Limb Profiler instrument. The tomographic retrieval substantially improves the agreement in magnitude and vertical structure with coincident lidar and occultation observations compared to the standard retrieval. We also show a secondary effect of bias from uncertainty in assumed particle size distribution parameters that results in a systematic underestimation of the aerosol extinction in the altitude region of the peak of the volcanic aerosol layer.

Speaker: Adam Bourassa (University of Saskatchewan)

10:30 → 11:00 Coffee break

11:00 → 11:20 Aerosol and clouds: profiles, composition, trends

11:00 Climate Data Record of Stratospheric Aerosols

Climate-related studies need information about the distribution of stratospheric aerosols, which impact the energy balance of the Earth’s atmosphere. In this work, we present a merged dataset of vertically resolved stratospheric aerosol extinction coefficients, which is derived from data by six limb and occultation satellite instruments: SAGE II on ERBS, GOMOS and SCIAMACHY on Envisat, OSIRIS on Odin, OMPS on Suomi-NPP, and SAGE III on International Space Station.
The merging of aerosol profiles is performed by transformation of the aerosol datasets from individual satellite instruments to the same wavelength, i.e., 750 nm, and their de-biasing and homogenization by adjusting the seasonal cycles. After such homogenization, the data from individual satellite instruments are in good agreement. The merged aerosol extinction coefficient is computed as the median of the adjusted data from the individual instruments.
The merged time series of vertically resolved monthly mean aerosol extinction coefficients at 750 nm is provided in 10° latitudinal bins from 90°S to 90°N, in the altitude range from 8.5 km to 39.5 km. The time series of the stratospheric aerosol optical depth (SAOD) is created by integration of aerosol extinction profiles from the tropopause to 39.5 km; it is also provided as monthly mean data in 10° latitudinal bins. The created aerosol climate record covers the period from October 1984 until May 2022, and it is intended to be extended in the future. It can be used in various climate-related studies.

Speaker: Viktoria Sofieva (Finnish Meteorological Institute)

11:20 → 11:40 Emissions: techniques, algorithms, products

11:20 Deployment of the CAIRT airborne demonstrator GLORIA on stratospheric balloon

The Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) is a limb-imaging Fourier-Transform spectrometer (iFTS) providing mid-infrared spectra with high spectral resolution (0.0625 cm-1 in the wavelength range 780-1400 cm-1). GLORIA, a demonstrator for the Changing-Atmosphere Infra-Red Tomography Explorer (CAIRT, one of the candidates selected for Phase 0 for the ESA Earth Explorer 11 mission) was deployed on the Russian M55 Geophysica and is still being deployed on HALO, the German high-altitude research aircraft. In order to enhance the vertical range of GLORIA to observations in the middle stratosphere albeit still reaching down to the middle troposphere, the instrument was adapted to measurements from stratospheric balloon platforms. GLORIA-B performed its first flight from Kiruna (northern Sweden) in August 2021 and its second flight from Timmins (Ontario/Canada) in August 2022 in the framework of the EU Research Infrastructure HEMERA.
The objectives of GLORIA-B observations for these campaigns have been primarily its technical qualification and the provision of a first imaging hyperspectral limb-emission dataset from 5 to 36 km altitude as well as scientific objectives, which are, amongst others, the observation of the evolution of the upper tropospheric and stratospheric chlorine and nitrogen budget/family partitioning in a changing climate in combination with the set of 20 MIPAS-B (Michelson Interferometer for Passive Atmospheric Sounding - Balloon) flights from 1995 to 2014, the observation of the BrONO2 evolution during sunset and sunrise, in synergy with BrO observations by the TotalBrO instrument (Univ. Heidelberg) on the same gondola, as well as the quantification of pollution of the Arctic and mid-latitude upper troposphere/lower stratosphere through forest fires.
In this contribution we will demonstrate the performance of GLORIA-B with regard to level-2 data, consisting of retrieved altitude profiles of a variety of trace gases. We will show examples of selected results together with uncertainty estimations, altitude resolution as well as comparisons with externally available datasets.

Speaker: Gerald Wetzel (Karlsruhe Institute of Technology)

11:40 → 12:00 Closing speech